55 Jewelers Park Drive
Neenah WI 54956

February 11, 2008

VIA EDGAR

Mr. Stephan Krikorian
Accounting Branch Chief
Mail Stop 4561
Securities and Exchange Commission
100 F Street, NE
Washington DC 20549

RE: Plexus Corp.
Commission File No. 000-14824

Dear Mr. Krikorian:

     This letter responds to the comments which Commission Staff made in your letter dated January 29, 2008, addressed to Dean A. Foate, Plexus Corp.’s President and Chief Executive Officer, relating to Plexus’ fiscal 2007 Annual Report on Form 10-K and Form 8-K dated January 23, 2008. I am answering at Mr. Foate’s request. The response is made to the comments in numbered Paragraph 1 of your letter.

Plexus Response

     Plexus regularly uses after-tax return on invested capital (“ROIC”) as an internal management tool to evaluate performance, particularly to note year over year changes. Also, a derivative of ROIC (Return on Capital Employed — “ROCE”) is used as one of the key components under Plexus’ annual variable incentive compensation plan. We chose to provide this information to investors because we believe it provides insight into the metrics that are driving management as well as management’s performance under the tests which it sets for itself. In particular, we believed it was an important disclosure to shareholders in 2007, when ROIC showed a decline from the prior year, to continue consistent disclosure. We also provide this disclosure because we believe investors find it to be a useful measurement.

     Since Plexus views ROIC as a ratio of performance and not a “GAAP” disclosure, we did not consider the inclusion of ROIC comparisons to be a “non-GAAP” disclosure that would require reconciliation to a “GAAP” ratio. Rather, we considered ROIC as an internal ratio that is

Mr. Stephan Krikorian
February 11, 2008
Page 2

prepared from data and other information to compare changes from period to period. We have reviewed the definition of non-GAAP financial measures and the discussion of them in Release 33-8176, and now have a better appreciation for why the Staff would consider our ROIC presentation to be a non-GAAP disclosure. We will treat it accordingly on a going-forward basis.

     In the Form 10-K, we included a table and a definition to explain our computation of ROIC, with the intent of making the ratio more understandable to readers. We also provided the discussion of ROIC after our discussion of key GAAP metrics to not unduly highlight ROIC. Going forward, we will be mindful of the provisions of Regulation S-K, Item 10(e). As requested by the Staff, set forth on Appendix A is a reconciliation of the ROIC numbers which we presented.

     On a going forward basis, we will provide a more thorough explanation of why we use ROIC internally. We will also augment the information which we provide regarding the calculation of ROIC; for example, to the extent we use any adjusted numbers in its calculation, we will begin our calculation with numbers prior to any adjustment and show the changes in a manner similar to but abbreviated from the reconciliation attached to our quarterly earnings press releases. We will further consider whether there is a GAAP ratio to which we should specifically reconcile the ROIC information; however, we have not at this point determined one that we believe is reasonably comparable.

*       *       *

     On behalf of Plexus, and as requested in your letter, we acknowledge that:

• Plexus is responsible for the adequacy and accuracy of the disclosure in its filings;

• Staff comments or changes in disclosure in response to Staff comments in the filings reviewed by the Staff do not foreclose the Commission from taking any action with respect to the filing; and

• Plexus may not assert Staff comments as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

Mr. Stephan Krikorian
February 11, 2008
Page 3

     We trust that you will find this letter responsive to your comments. Please feel free to contact me at (920) 751-5487, Angelo M. Ninivaggi, Plexus’ General Counsel, at (920) 751-3524, or Kenneth V. Hallett of Quarles & Brady LLP, our outside counsel, at (414) 277-5345, if you have any questions or need further information.

Very truly yours, PLEXUS CORP.
By:	/s/ Ginger M. Jones
	Ginger M. Jones
	Vice President and Chief Financial Officer

cc: Mr. Dean A. Foate
Angelo M. Ninivaggi, Esq.
Kenneth V. Hallett, Esq.

Appendix A

ROIC calculation with non-GAAP numbers

	Quarter ended		Fiscal year ended
	December 29,		September 29,		September 30,		October 1,
	2007		2007		2006		2005
Operating income	$	31,928	$	79,438	$	80,262	$	(9,745	)
Plus unusual charges (restructuring and/or impairment)		—		1,838		—		39,162
Operating income (excluding unusual charges)		31,928		81,276		80,262		29,417
Tax rate (excluding unusual charges)		18.0%		22.0%		0.6%		5.0%
Income taxes — Non-GAAP		5,747		17,881		482		1,471
Operating income (tax effected)	$	26,181	$	63,395	$	79,780	$	27,946
Average capital employed	$	404,600	$	360,308	$	277,033	$	321,611
ROIC		25.9%		17.6%		28.8%		8.7%

	Actual			Actual			Average capital
	9/29/07			12/29/2007			employed
Equity	$	573,265		$	604,792
Plus:
Debt — current		1,720			1,815
Debt — non-current		25,082			24,681
Less:
Cash and cash equivalents		(154,109	)		(158,547	)
Short-term investments		(55,000	)		(54,500	)
	$	390,958		$	418,241		$	404,600

	Actual			Actual			Actual			Actual			Actual			Average capital
	9/30/06			12/30/06			3/31/07			6/30/07			9/29/07			employed
Equity	$	481,567		$	503,457		$	518,023		$	540,437		$	573,265
Plus:
Debt — current		997			1,049			1,643			1,701			1,720
Debt — non-current		25,653			25,739			25,551			25,460			25,082
Less:
Cash and cash equivalents		(164,912	)		(132,872	)		(132,706	)		(145,206	)		(154,109	)
Short-term investments		(30,000	)		(45,000	)		(45,000	)		(45,000	)		(55,000	)
	$	313,305		$	352,373		$	367,511		$	377,392		$	390,958		$	360,308

	Actual			Actual			Actual			Actual			Actual			Average capital
	10/1/05			12/31/05			4/1/06			7/1/06			9/30/06			employed
Equity	$	340,015		$	356,629		$	393,111		$	437,038		$	481,567
Plus:
Debt — current		770			1,758			1,553			1,245			997
Debt — non-current		22,310			21,959			21,623			21,666			25,653
Less:
Cash and cash equivalents		(98,727	)		(109,667	)		(124,673	)		(139,750	)		(164,912	)
Short-term investments		(10,000	)		(10,000	)		(25,000	)		(30,000	)		(30,000	)
	$	254,368		$	260,679		$	266,614		$	290,199		$	313,305		$	277,033

	Actual			Actual			Actual			Actual			Actual			Average capital
	9/30/04			1/1/05			4/2/05			7/2/05			10/1/05			employed
Equity	$	351,413		$	358,819		$	352,722		$	326,759		$	340,015
Plus:
Debt — current		811			2,744			2,077			1,165			770
Debt — non-current		23,160			29,912			22,638			22,523			22,310
Addback of goodwill written-off											26,915			26,915
Less:
Cash and cash equivalents		(40,924	)		(43,614	)		(36,119	)		(64,225	)		(98,727	)
Short-term investments		(4,005	)		—			—			(6,000	)		(10,000	)
	$	330,455		$	347,861		$	341,318		$	307,137		$	281,283		$	321,611

Appendix A

ROIC calculation with GAAP numbers

	Quarter ended		Fiscal year ended
	December 29,		September 29,		September 30,			October 1,
	2007		2007		2006			2005
Operating income	$	31,928	$	79,438	$	80,262		$	(9,745	)
Tax rate		18.0%		22.0%		-20.6%			-12.9%
Income taxes — GAAP		5,747		17,476		(16,534	)		1,257
Operating income (tax effected)	$	26,181	$	61,962	$	96,796		$	(11,002	)
Average capital employed	$	404,600	$	360,308	$	277,033		$	310,845
ROIC		25.9%		17.2%		34.9%			-3.5%

	Actual			Actual			Average capital
	9/29/07			12/29/2007			employed
Equity	$	573,265		$	604,792
Plus:
Debt — current		1,720			1,815
Debt — non-current		25,082			24,681
Less:
Cash and cash equivalents		(154,109	)		(158,547	)
Short-term investments		(55,000	)		(54,500	)
	$	390,958		$	418,241		$	404,600

	Actual			Actual			Actual			Actual			Actual			Average capital
	9/30/06			12/30/06			3/31/07			6/30/07			9/29/07			employed
Equity	$	481,567		$	503,457		$	518,023		$	540,437		$	573,265
Plus:
Debt — current		997			1,049			1,643			1,701			1,720
Debt — non-current		25,653			25,739			25,551			25,460			25,082
Less:
Cash and cash equivalents		(164,912	)		(132,872	)		(132,706	)		(145,206	)		(154,109	)
Short-term investments		(30,000	)		(45,000	)		(45,000	)		(45,000	)		(55,000	)
	$	313,305		$	352,373		$	367,511		$	377,392		$	390,958		$	360,308

	Actual			Actual			Actual			Actual			Actual			Average capital
	10/1/05			12/31/05			4/1/06			7/1/06			9/30/06			employed
Equity	$	340,015		$	356,629		$	393,111		$	437,038		$	481,567
Plus:
Debt — current		770			1,758			1,553			1,245			997
Debt — non-current		22,310			21,959			21,623			21,666			25,653
Less:
Cash and cash equivalents		(98,727	)		(109,667	)		(124,673	)		(139,750	)		(164,912	)
Short-term investments		(10,000	)		(10,000	)		(25,000	)		(30,000	)		(30,000	)
	$	254,368		$	260,679		$	266,614		$	290,199		$	313,305		$	277,033

	Actual			Actual			Actual			Actual			Actual			Average capital
	9/30/04			1/1/05			4/2/05			7/2/05			10/1/05			employed
Equity	$	351,413		$	358,819		$	352,722		$	326,759		$	340,015
Plus:
Debt — current		811			2,744			2,077			1,165			770
Debt — non-current		23,160			29,912			22,638			22,523			22,310
Less:
Cash and cash equivalents		(40,924	)		(43,614	)		(36,119	)		(64,225	)		(98,727	)
Short-term investments		(4,005	)		—			—			(6,000	)		(10,000	)
	$	330,455		$	347,861		$	341,318		$	280,222		$	254,368		$	310,845