Analysis of the enzymes produced by clinical isolates of multiresistant Klebsiella pneumoniae from hospitals in France revealed two novel broad-spectrum beta-lactamases. The first, characterized by an isoelectric point of 6.3 and a high hydrolytic activity on cefotaxime, is designated CTX-1. This beta-lactamase was encoded by a 95-kilobase plasmid (incompatibility group 7M) and cotransferred with resistance to tetracyclines, sulfonamides, and aminoglycosides (AAC [6']-IV). From 1984 to June 1987, 490 CTX-1-producing strains of Enterobacteriaceae were isolated. The second plasmid-mediated beta-lactamase (CAZ-1) was isolated in 1987 from three K. pneumoniae strains more resistant to ceftazidime than to other third-generation cephalosporins. This broad-spectrum beta-lactamase differed from CTX-1 by its isoelectric point--close to 5.6--and its high hydrolytic activity on ceftazidime and was encoded by a 150-kilobase plasmid. It was demonstrated that these expanded-spectrum beta-lactamases are TEM derivatives.