The combination aztreonam + cefotaxime (AZ + CE) was compared to amikacin + cefotaxime (AM + CE) in the treatment of nosocomial pneumonia acquired at the intensive-care unit. This study included a total of 33 patients fulfilling criteria for nosocomial pneumonia. 16 of them were randomly allocated to the AZ + CE group and 17 to the AM + CE group. The empirical treatment was effective for 78% of AZ + CE cases and 92% of AM + CE cases (p = NS). Clinical cure was observed in 77% of cases (10 out of 13 evaluable) in the AZ group and in 75% of the group treated with AM (12 cases out of 16 evaluable; p = NS). In the evaluable cases, treatment failure was associated with injections due to the following organisms: Acinetobacter calcoaceticus (1) and Pseudomonas aeruginosa (1) in the AZ group and A. calcoaceticus (1) in the AM group. Superinfections were observed only in the AM group P. aeruginosa, A. calcoaceticus, Streptococcus viridans, Candida albicans, Aspergillusfumigatus and Serratiamar-cescens. Both the peak and through serum concentrations of AZ and AM were maintained within normal ranges. Finally, an impairment of renal tubular function was observed in the group of patients treated with AM, as measured by urinary levels of N-ace-tyl-β-D-glucosaminidase and leucine aminopeptidase sequentially during the treatment. These changes in renal functions alterations mentioned were not observed in the AZ group. It is concluded that the AZ + CE combination is an effective empirical and active antibiotic treatment against severe nosocomial pneumonia. Aztreonam has no renal toxicity, which is an advantage to take into account in patients with altered renal function