Cefpirome (CPO) is a new broad-spectrum cephalosporin, with a better activity against Grampositive cocci, Pseudomonas spp. and Acinetobacter spp. than cefotaxime. The aim of this study was to determine the efficacy and tolerance of CPO for the treatment of severe Gram-negative infections in ICU patients. 88 observations of bacteriologically documented pneumonia, peritonitis, pyelonephritis and septicemia in 86 ICU patients were recorded. Antibiotherapy was given before microbiological results became available, and consisted of CPO 2 g and amikacin 10 mg/kg administered b.i.d. Doses were adapted when required by renal failure. Definitive inclusion was obtained when ampicillin resistance and CPO susceptibility were determined for the Gram-negative bacilli isolated. Tolerance was then analysed for all 86 patients, although efficacy was evaluated only for 28 patients. Among 102 isolated pathogens, CPO activity was determined for 82 cases and was effective against 71 (86.5%). Clinical efficacy was obtained for 18 of 28 patients (64%), and bacteriological results were considered effective for 20 of 27 cases (74%), 1 case remaining undetermined. As regards tolerance at least one adverse effect was reported for 43 patients (50%). Among the 62 reported adverse effects, only 6 (2 cutaneous rashes, 4 biological abnormalities) were considered to be possibly related to CPO. In none of these cases, was the treatment discontinued. The results of this study confirm the efficacy of CPO, initially combined with amikacin, for the treatment of severe Gram-negative resistant bacilli infections in ICU patients.