A randomized, double-blinded, controlled clinical study of 84 patients with surgically treated gangrenous or perforated appendicitis was done to compare the efficacy of the combination of aztreonam, the first monobactam antibiotic, with gentamicin when either was combined with clindamycin. Fifty-six patients who were treated with aztreonam and clindamycin (A/C) and 28 patients who were treated with gentamicin and clindamycin (G/C) fulfilled criteria for evaluation. A matched historic control group of 56 G/C patients was also included for comparison. All measures of outcome, including days of fever, hospitalization, antibiotic therapy, and the incidence of antibiotic failures, were similar. It was concluded that aztreonam was as effective as gentamicin in this study and may offer some advantages with regard to toxicity and serum drug level monitoring.