Document And Entity Information - shares	3 Months Ended
	Dec. 31, 2020	Feb. 05, 2021
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Registrant Name	BIOANALYTICAL SYSTEMS INC
Entity Current Reporting Status	Yes
Entity Central Index Key	0000720154
Current Fiscal Year End Date	--09-30
Entity Filer Category	Non-accelerated Filer
Trading Symbol	BASi
Entity Common Stock, Shares Outstanding		11,131,256
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Shell Company	false
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Shares