For 256 of the 338 patients in a multicenter study treated with imipenem/cilastatin (mean daily dosage, 1.6 g per day; mean duration of treatment, 8.5 days) for a variety of infections, 286 infections were microbiologically proven. Clinical cure was achieved in 216 of these infections and improvement, in 18. Ninety-eight of these infections were classified as severe or moderately severe. The infecting pathogen was eradicated in 79% of the infections. Therapy with imipenem/cilastatin was discontinued in 10(3%) of 338 patients because of adverse gastrointestinal effects. Pathologic laboratory parameters were reported for 28 patients (8%); in only one patient with thrombocytopenia was therapy discontinued. Renal tolerance of imipenem/cilastatin was good, and no nephrotoxicity was observed. From the susceptibility tests available for 452 bacterial strains, a susceptibility breakpoint of less than or equal to 8 micrograms/ml is recommended.