A review is given of work utilizing the serum bactericidal test for preclinical evaluation of agents considered for treatment of gram-negative sepsis among neutropenic cancer patients. Following a description of the methodology of the two major groups, the results of the various antibiotic trials are summarized. First the extended-spectrum cephalosporins (cefotaxime, cefoperazone, and moxalactam) were tested and found to be, at best, of limited value as single agents for Pseudomonas aeruginosa, a common pathogen of neutropenic cancer patients. When the extended-spectrum penicillins became available, the serum bactericidal levels in volunteers of mezlocillin and piperacillin were compared alone or in combination with an aminoglycoside to ticarcillin with or without aminoglycoside against the same organisms. Piperacillin proved to be most effective followed by mezlocillin and then ticarcillin; in each case the addition of the aminoglycoside improved serum bactericidal activity. Recent studies suggest that imipenem alone is as active as the combination of a broad-spectrum penicillin plus an aminoglycoside and is worthy of a carefully controlled clinical trial. These types of volunteer-based evaluations of the serum bactericidal activity of new compounds may help predict useful clinical approaches for the future.