4-aminobenzoic acid, a factor in the vitamin B complex, required for biosynthesis of folate; neutralizes the bacteriostatic effects of the sulfonamides because it furnishes an essential growth factor for bacteria; elevated concentrations of the sulfonamides interfere with use of this agent and of folates; used as an ultraviolet screen in lotions and creams. It is produced in a test of pancreatic function. SYN: paraaminobenzoic acid, vitamin Bx.