The parenteral kinetics of sulbactam, a potent synergist with ampicillin against a broad range of clinically important organisms in humans, are similar to those of ampicillin. The kinetics of ampicillin were not affected by co-administration of sulbactam, and high levels of both agents were attained: 15-min infusions of 2 g of ampicillin plus 1 g of sulbactam produced peak serum concentrations of approximately 120 micrograms of ampicillin/ml plus 60 micrograms of sulbactam/ml; intramuscular injections of 1 g of ampicillin plus 0.5 g of sulbactam produced peak concentrations of 18 micrograms of ampicillin/ml plus 13 micrograms of sulbactam/ml. The drugs had similar half-lives (approximately 1 hr), and both drugs were excreted primarily in the urine (greater than 75%). Although the kinetics of sulbactam in postpartem women and in surgical patients were similar to the kinetics in young men, the half-life of sulbactam (like that of ampicillin) was altered in the elderly, during labor, in neonates, and in patients with renal impairment. After distribution of the agents in the body, the concentrations of both drugs in blister and parenteral fluid were similar to those in serum. Furthermore, useful antibacterial concentrations of both drugs were found in pus, sputum, and middle-ear fluid. The normally low penetration of sulbactam and ampicillin into cerebrospinal fluid was increased in patients with bacterial meningitis.