SCHEDULE 13G

Amendment No. 6
Genentech Incorporated
Special Common Stock
Cusip # 368710307

Cusip # 368710307
Item 1:	Reporting Person - FMR Corp.
Item 4:	Commonwealth of Massachusetts
Item 5:	2,300
Item 6:	0
Item 7:	2,300
Item 8:	0
Item 9:	2,300
Item 11:	0.004%
Item 12:	    HC

Cusip # 368710307
Item 1:	Reporting Person - Edward C. Johnson 3d
Item 4:	United States of America
Item 5:	0
Item 6:	0
Item 7:	2,300
Item 8:	0
Item 9:	2,300
Item 11:	0.004%
Item 12:	IN

Cusip # 368710307
Item 1:	Reporting Person - Abigail P. Johnson
Item 4:	United States of America
Item 5:	None
Item 6:	None
Item 7:	2,300
Item 8:	None
Item 9:	2,300
Item 11:	0.004%
Item 12:	    IN


SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)


Item 1(a).	Name of Issuer:

		Genentech Incorporated

Item 1(b).	Name of Issuer's Principal Executive Offices:

		460 Point San Bruno Boulevard,
		South San Francisco, CA  94080-4918

Item 2(a).	Name of Person Filing:

		FMR Corp.

Item 2(b).	Address or Principal Business Office or, if None,
Residence:

		82 Devonshire Street, Boston, Massachusetts  02109

Item 2(c).	Citizenship:

		Not applicable

Item 2(d).	Title of Class of Securities:

		Special Common Stock

Item 2(e).	CUSIP Number:

		368710307

Item 3.	This statement is filed pursuant to Rule 13d-1(b) or 13d-
2(b) and the person filing, FMR Corp., is a parent holding company in
accordance with Section 240.13d-1(b)(ii)(G).  (Note:  See Item 7).

Item 4.	Ownership

	(a)	Amount Beneficially Owned:	2,300

	(b)	Percent of Class:	0.004%

	(c)	Number of shares as to which such person has:

	(i)	sole power to vote or to direct the vote:	2,300

	(ii)	shared power to vote or to direct the vote:	0

	(iii)	sole power to dispose or to direct the disposition of:
	2,300

	(iv)	shared power to dispose or to direct the disposition of:
	0




Item 5.	Ownership of Five Percent or Less of a CommonStock.

	If this statement is being filed to report the fact that as of
the date hereof, the reporting person has ceased to be the beneficial
owner of more than five percent of the class of securities, check the
following (X).

Item 6.	Ownership of More than Five Percent on Behalf of Another
Person.

	Not applicable

Item 7.	Identification and Classification of the Subsidiary Which
Acquired the Security Being Reported on By the Parent Holding Company.

	See attached Exhibit(s) A, B.

Item 8.	Identification and Classification of Members of the Group.

	Not applicable. See attached Exhibit A.

Item 9.	Notice of Dissolution of Group.

	Not applicable.

Item 10.	Certification.

	Inasmuch as the reporting persons are no longer the beneficial
owners of more than five percent of the number of shares outstanding,
the reporting persons have no further reporting obligation under
Section 13(d) of the Securities and Exchange Commission thereunder, and
the reporting persons have no obligation to amend this Statement if any
material change occurs in the facts set forth herein.

Signature

	After reasonable inquiry and to the best of my knowledge and
belief, I certify that the information set forth in this Schedule 13G
in connection with FMR Corp.'s beneficial ownership of the Special
Common Stock of Genentech Incorporated at June 30, 1999 is true,
complete and correct.

	July 10, 1999
Date


	/s/Eric D. Roiter
Signature


	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of FMR Corp. and its direct and indirect
	subsidiaries



SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)

	Fidelity Management Trust Company, 82 Devonshire Street, Boston,
Massachusetts 02109, a wholly-owned subsidiary of FMR Corp. and a bank
as defined in Section 3(a)(6) of the Securities Exchange Act of 1934,
is the beneficial owner of  2,300 shares or 0.004% of the Special
Common Stock outstanding of the Company as a result of its serving as
investment manager of the institutional account(s).

	Edward C. Johnson 3d and FMR Corp., through its control of
Fidelity Management Trust Company, each has sole dispositive power over
2,300 shares and sole power to vote or to direct the voting of 2,300
shares of Special Common Stock owned by the institutional account(s) as
reported above.

	Members of the Edward C. Johnson 3d family are the predominant
owners of Class B shares of common stock of FMR Corp., representing
approximately 49% of the voting power of FMR Corp.  Mr. Johnson 3d owns
12.0% and Abigail Johnson owns 24.5% of the aggregate outstanding
voting stock of FMR Corp.  Mr. Johnson 3d is Chairman of FMR Corp. and
Abigail P. Johnson is a Director of FMR Corp.  The Johnson family group
and all other Class B shareholders have entered into a shareholders'
voting agreement under which all Class B shares will be voted in
accordance with the majority vote of Class B shares.  Accordingly,
through their ownership of voting common stock and the execution of the
shareholders' voting agreement, members of the Johnson family may be
deemed, under the Investment Company Act of 1940, to form a controlling
group with respect to FMR Corp.





SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)
RULE 13d-1(f)(1)  AGREEMENT

	The undersigned persons, on July 10, 1999, agree and consent to
the joint filing on their behalf of this Schedule 13G in connection
with their beneficial ownership of the Special Common Stock of
Genentech Incorporated at June 30, 1999.

FMR Corp.

By   /s/Eric D. Roiter
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of FMR Corp. and its direct and indirect
	subsidiaries

Edward C. Johnson 3d

By   /s/Eric D. Roiter
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of Edward C. Johnson 3d

Abigail P. Johnson

By   /s/Eric D. Roiter
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of Abigail P. Johnson