Thirty-five patients underwent 38 treatment courses with cefotaxime. Documented infections included 11 bacteremias, 7 cases of nosocomial pneumonia, 6 surgical wound infections, 3 bone infections, 1 biliary infection, and 1 urinary tract infection. Granulocytopenic patients with fever received 15 courses of empiric cefotaxime therapy alone; in 8 courses, no definite site of infection or pathogen was isolated. Broad-spectrum antibiotics had been administered to 23 patients before cefotaxime. Thirty-seven bacterial pathogens were isolated from 25 patients. Three such pathogens were resistant to cefotaxime and required alternative therapies. Pathogenic isolates included 13 Serratia marcescens, 12 Pseudomonas aeruginosa, 4 Escherichia coli, 2 Klebsiella pneumoniae, 2 Providencia stuartii, 1 Enterobacter cloacae, 1 Haemophilus influenzae, 1 Enterococcus, and 1 Staphylococcus aureus. Of the treatment courses, 25 of 38 resulted in a favorable response to cefotaxime, including 9 of 15 in granulocytopenic patients. Superinfection was seen in one patient. The emergence of resistance was documented in another patient. Of 15 patients with multiply resistant pathogens, 12 improved with cefotaxime. Of 12 patients with Pseudomonas aeruginosa, 6 favorably responded. Possible complications of cefotaxime were observed in 14 of 42 treatment courses. Cefotaxime is most useful in treatment of infections due to multiply resistant, gram-negative pathogens other than Pseudomonas aeruginosa.