We report the first example of a monoclonal antibody-catalysed hydrolysis of a P-lactam where the antibodies were generated by a simple transition-state analogue. A rat monoclonal antibody (1/91c/4d/26) generated by using an acyclic 4-nitrophenylphosphate immunogen catalysed the hydrolysis of corresponding 4-nitrophenyl carbonates but, more importantly. also catalysed the hydrolysis of N-(4-nitrophenyl)-azetidinone at pH 8 with k(cat) = 8.7 x 10(-6) s(-1) and K-M = 35 muM. This is the first example of a rat monoclonal catalytic antibody. (C) 2002 Elsevier Science (USA). All rights reserved.