Background. A prospective, randomized, single-blind study evaluated the efficacy and safety of clindamycin plus amikacin versus clindamycin plus aztreonam (Cl-Az) in treating intraabdominal infections in adults. Methods. Patients were treated intravenously for 7 to 10 days, clindamycin 900 mg plus amikacin 5.0 mg/kg three times a day or clindamycin 900 mg plus aztreonam 2.0 gm three times a day. All 67 patients enrolled were evaluated for safety and 31 in each group for clinical and microbiologic response. Both groups were similar in initial diagnosis, perforated appendicitis or intraabdominal abscess. In each group 24 patients (77%) were admitted in serious condition and three (10%) in critical condition. Twenty-five patients (80.6%) in each group had aerobic and anaerobic pathogens; the remainder had either aerobic or anaerobic pathogens. Results. On therapy completion, clinical and bacteriologic responses were as follows: clindamycin plus amikacin group, 26 (84%) cured, 3 (9.7%) improved, and 2 (6.3%) failed; Cl-Az group, 26 (80.7%) cured, 6 (19.3%) improved, and 0 failed. Rapid temperature decrease occurred in Cl-Az group (p = 0.007). Forty-one mild adverse medical events reported were evenly distributed, but no patients were removed as a result. Conclusions. Both combinations were highly effective in managing intraabdominal sepsis. Clindamycin aztreonam showed a slight advantage because of absence of renal toxicity and shorter time to apyrexia.