The effect of topical ampicillin sodium and polyglycolic acid and silk sutures on the recurrence of an existing hernia or an incisional hernia and on infection rates in clean abdominal wounds (herniotomies and simple cholecystectomies) was studied in a triple-blind, randomized trial with 398 consecutive patients. One infection, three suture sinuses, and two incisional hernias occurred among 113 patients with cholecystectomies, while the corresponding rates in 285 patients with hernia repairs were 11 infections, no suture sinuses, and three recurrent hernias. No effect of ampicillin could be demonstrated, nor was any difference between polyglycolic acid and silk sutures shown. No interaction between the antibiotic and suture material was found, and no side effects were observed. Wound infection was significantly more frequent in patients with postoperative seromas or hematomas.