The expression of penicillin acylase (PA), cloned in the pPA102 plasmid under control of the wild-type lac promoter and using galactose as inducer in Escherichia coli JM101, JM103 and JM105 transformant cells, was analyzed. The E. coli JM101/pPA102 cultures attained the highest specific activity of PA. For large scale PA production based on E. coli JM101/pPA102 a culture media with galactose instead of isopropyl-thio-galactopyranoside as inducer would be as successful and less expensive.