The comparative in vitro activity of amikacin, cefamandole, cefoperazone, cefotaxime, cefoxitin, cephalothin, chloramphenicol, moxalactam, piperacillin, ticarcillin and tobramycin against 170 community blood culture isolates of gram-negative bacilli was investigated using the quantitative plate dilution method. Results showed that amikacin, cefoperazone, cefotaxime, moxalactam, piperacillin and tobramycin were most active on a weight basis. Tobramycin and amikacin were quite active against Pseudomonas aeruginosa but one isolate showed an MIC of 50 μg/ml to both. The order of activity of the remaining drugs for P. aeruginosa ticarcillin