A prospective randomized trial was performed to determine the value of tetracycline lavage in addition to systemic antibiotic prophylaxis in 159 patients undergoing elective and emergency intestinal operations. Tetracycline lavage was associated with a significant overall reduction in postoperative infection rates in 25 of 74 patients (34 percent) receiving saline lavage compared with 15 of 85 patients (18 percent) having tetracycline lavage (P<0.05). Tetracycline lavage was associated with a significant reduction in the counts of aerobic and anaerobic bacteria in the peritoneal fluid at the end of the operation (P<0.05 andP<0.01, respectively) and with a significant reduction of aerobes 24 hours postoperatively (P<0.02). Tetracycline lavage would appear to confer clinical benefit in preventing postoperative infection.