We compared ceftazidime with moxalactam, a commonly utilized, currently available drug. The microbiological activities of ceftazidime and moxalactam were studied. In addition, single-dose pharmacokinetics and serum bactericidal activity 1 and 6 h after a 2.0-g, 30-min infusion of each drug were determined in a crossover study in human volunteers. In vitro, both drugs had MICs for 90% of the isolates of less than 1.0 microgram/ml against the common members of the family Enterobacteriaceae and of 8.0 micrograms/ml against Staphylococcus aureus. Against Pseudomonas aeruginosa ceftazidime was more active than moxalactam, the respective MICs for 90% of the isolates being 8 and 128 micrograms/ml. Mean half-lives were 1.75 (+/- 0.21) h for ceftazidime and 2.5 (+/- 0.38) h for moxalactam. The serum bactericidal titers for both compounds against Escherichia coli and Klebsiella pneumoniae were high. Titers against S. aureus 6 h after infusion were negative. The mean (geometric) serum bactericidal titer of ceftazidime against 31 strains of P. aeruginosa (1:44) was higher than that of moxalactam (1:3.4).