Sixty-five episodes of nosocomial infections of the blood, lungs, urinary tract, soft tissues, bones, or central nervous system were treated with intravenous moxalactam (3-12 g per day). Bacteremia was documented in 21 patients. Despite the severely compromised condition of many patients, 80% of the infections responded satisfactorily, as defined by clinical and microbiologic cure or improvement. Of the 21 cases of nosocomial bacteremia, 14 (67%) responded satisfactorily. Of the six cases of bacteremia caused by gram-negative bacilli resistant to aminoglycosides, three responded satisfactorily. Moxalactam therapy also resulted in cure or improvement in nine (69%) of 13 pulmonary infections, and it was used alone to cure one case of meningitis-ventriculitis due to Klebsiella pneumoniae. Seven of 13 therapeutic failures involved Pseudomonas aeruginosa, and moxalactam-resistant P. aeruginosa emerged during therapy for 12 patients. Adverse effects, usually mild diarrhea, occurred in 9.2% of the patients. Except for some severe infections due to P. aeruginosa, moxalactam is effective and safe therapy for nosocomial infections caused by susceptible organisms.