Penicillin V acylase (PVA) used in the production of 6-aminopenicillanic acid (6-APA) and 7-aminodesacetoxycephalosporanic acid (7-ADCA) is produced by a wide range of microorganisms. Both traditional mutagenic and modern genetic engineering techniques are applied to isolate the strains producing large amounts of PVA. Productivity as high as 3,200 U g(-1) dry cell weight is achieved. Comparison of the physicochemical properties of purified enzyme preparations indicate a wide variation; however, in general the PVAs are specific for phenoxyacetyl amides of beta-lactam molecules and very few enzymes hydrolyze other phenoxyacetyl derivatives. Both immobilized enzyme and cell preparations are developed for production of 6-APA and 7-ADCA. The advantages of PVA in the production of 6-APA are discussed.