&NA;In a prospective, randomized control trial, 152 consecutive patients requiring emergency or complicated colorectal surgery were allocated either to two doses of cefotetan or to five‐day cover with gentamicin, and a single dose of metronidazole. Twenty‐one patients received 6 gm of cefotetan before prolongation of prothrombin time dictated a change in the dose regimen such that all remaining patients (N=55) received only 4 gm of cefotetan. The groups were well matched for diagnosis and surgical procedure. Rates of postoperative infection did not differ significantly between the groups, with wound infection rates occurring in 17 of 75 patients receiving gentamicin and metronidazole (22.7 percent) compared with ten of 75 receiving cefotetan (13 percent). Although wound infection rates were lower in the cefotetan group, the incidence of intra‐abdominal abscess was similar in both groups. Eight patients receiving cefotetan developed intra‐abdominal abscesses (11 percent), compared with seven receiving gentamicin and metronidazole (9 percent). Prolongation of prothrombin time in excess of 13 seconds occurred in six patients receiving cefotetan compared with no patients receiving gentamicin and metronidazole. None of these patients developed clinical bleeding, however.