The pharmacokinetics of the monobactam carumonam (Ro 17-2301) as derived from serial measurement of the concentrations of this agent in serum, blister fluid, and urine were studied in six male volunteers subsequent to intravenous infusion of a single 2-g dose. Drug levels in serum in excess of 75 micrograms/ml were achieved 0.5 h after the end of infusion, declining to 2.9 micrograms/ml at 8 h. The mean serum and blister fluid elimination half-lives were 1.68 and 1.7 h, respectively. The urinary recovery of the drug by 24 h was 80.6% (range, 68.3 to 91.1%). Carumonam penetrated blister fluid well, the mean percentage penetration (as measured by the ratio of areas under curves) being 101.6%.