Lysobacter enzymogenes produces an inducible beta-lactamase and induction with 100 micrograms ampicillin ml-1 resulted in an increase of more than 100-fold in enzyme activity. Various other beta-lactam antibiotics also served as effective inducers. The enzyme was obtained from cells by osmotic shocking to release periplasmic components and it was purified primarily by ion-exchange chromatography and PAGE. The beta-lactamase consists of one polypeptide with a molecular mass of about 28 kDa and an isoelectric point greater than 9.6. It is strongly inhibited by p-chloromercuribenzoate and clavulanic acid but not by EDTA. The enzyme readily hydrolyses several penicillins and cephalosporins, but not oxacillin or cloxacillin. The enzyme therefore belongs to group 2b of the bacterial beta-lactamases.