An open-label prospective, randomized, parallel multicentre study was undertaken to compare the efficacy and tolerability of 1.5 g/day intravenous imipenem/cilastatin with 3 g/day intravenous meropenem in the treatment of intra-abdominal infections. A total of 287 patients were enrolled: 201 patients, divided between the 2 treatment groups, were evaluable. Clinical outcome, bacteriological outcome, untoward microbiological effects, and clinical and laboratory adverse experiences were evaluated. 98% of patients receiving imipenem/cilastatin therapy were cured, with 96% showing eradication of infection. 95% of those on meropenem were cured, with 98% showing eradication. These differences in clinical and bacteriological outcome between the 2 treatments were not statistically significant. Two patients receiving imipenem/cilastatin and 5 receiving meropenem had untoward microbiological effects. There was a 0.7% frequency (1/139 patients) of possibly or probably drug-related clinical or laboratory adverse experiences with imipenem/cilastatin and a 2.7% frequency (4/148) with meropenem. The mean time to defervescence was significantly less for patients in the imipenem/cilastatin treatment group than for those receiving meropenem. This study shows that 1.5 g/day of imipenem/cilastatin is equivalent to 3.0 g/day meropenem in clinical and bacteriological outcome, as well as in incidence of side effects.