The disposition and metabolism of meropenem were studied in rats, dogs and cynomolgus monkeys following intravenous administration of [14C]-meropenem, and also in man following intravenous infusion of meropenem. Following intravenous administration to rats and dogs, radioactive material was very rapidly and widely distributed in the tissues, with highest levels detected in the kidney and other highly perfused organs. Concentrations in all tissues decreased rapidly with time. The plasma elimination half-life of meropenem was approximately 6 min in rats, 30 min in monkeys, 45 min in dogs and 1h in man. In all species 90-100% of the dose was excreted via the urine within 24 h. Analysis of the radioactive material in urine from animal studies showed that the major components were unchanged compound (36-43%) and a metabolite corresponding to a beta-lactam ring-opened form (34-51%). In man, approximately 65% of the dose was excreted in urine as unchanged meropenem and most of the remainder as the ring-opened metabolite. As part of the preclinical safety evaluation programme of meropenem, the distribution, metabolism and excretion of [14C]-meropenem were studied in the rat, dog and cynomolgus monkey after single intravenous administration at dose levels corresponding to the lower doses used in toxicity studies. In addition, the metabolism and pharmacokinetics of meropenem in human volunteers were studied.