Levels of moxalactam in serum of healthy volunteers after single intramuscular injection, slow bolus intravenous injection, or intravenous infusion were proportional to the dose given. After intravenous bolus injection of 1 g of moxalactam, the peak serum level was 201.0 micrograms/ml, the half-life (beta-phase) was 126 min, and the cumulative urinary excretion during a 10-hr period was 90.5% of the dose. The values for cefazolin in the same volunteers were similar to those for moxalactam. No accumulation of the drug in serum was found even after multiple intravenous injections of 1 g every 12 hr for five days. Probenecid administered orally did not significantly affect levels of moxalactam in serum or urinary recovery, an observation which suggests that renal excretion of moxalactam takes place mainly through glomerular filtration. The serum half-life (beta-phase) of moxalactam in subjects with a creatinine clearance rate of less than or equal to 10 ml/min was markedly prolonged. Concentrations of moxalactam in bile were higher than those of cefazolin in a crossover study. Concentrations in sputum were 1.84-2.11 micrograms/ml in individuals given 1 g by intravenous slow bolus injection. No active metabolite of moxalactam was detected in plasma or urine.