The combination of clindamycin plus a new semisynthetic cephalosporin, U63196E for which the United States approved name is cefpimizole, was tested against 47 aerobic Gram-negative rods and 30 aerobic Gram-positive cocci. Synergy was seen with Klebsiella pneumoniae (3 of 19 isolates) and Escherichia coli (2 of 21 isolates). All isolates of Pseudomonas aeruginosa, Staphylococcus aureus, methicillin-resistant Staph. aureus, and enterococci demonstrated either indifference or antagonistic reactions to the drug combination.