Cefotetan is a new cephamycin whose interaction with a group of eight beta-lactamases isolated from various Gram-negative bacteria has been studied. Using computerized micro-acidimetry, cefotetan was found to be resistant to the hydrolytic action of various enzymes, including those which actively hydrolyse cefotaxime. Despite this resistance to hydrolysis, cefotetan nevertheless shows a certain affinity for these enzymes. These data were submitted to two statistical procedures consisting of correspondence analysis and ascending hierarchical classification. These techniques revealed that cefotetan behaves very much like cefoxitin (another cephamycin) and also like cefotaxime and moxalactam.