&NA;A prospective, randomized, single‐blind, controlled clinical trial was undertaken to compare two different prophylactic antibiotic single‐dose regimens in patients undergoing elective colorectal surgery. Timentin, a combination of ticarcillin and clavulanic acid, was administered intravenously (3.1 g) to 87 patients. Mezlocillin, a semisynthetic penicillin was given intravenously (2.0 g) to 98 patients. The wound infection rate was 10.6 percent in patients receiving Timentin and 9.7 percent in those receiving mezlocillin (P>.05). Multivariate analysis of factors possibly affecting the wound infection rate showed that the presence of a colostomy preoperatively, fecal contamination at surgery, and the surgical group were the only factors that independently achieved a statistically significant association with the development of a postoperative wound infection in this trial (P<.0001).