Moxalactam disodium (Latamoxef), was evaluated as a single dose prophylactic antibiotic against wound infection in open colorectal surgery. One hundred and five consecutive patients admitted to the university department of surgery, Wellington Hospital, were studied. Twelve patients were excluded because either the antibiotic was not given or antibiotics were given for other reasons. Eleven patients developed early wound infections and one further patient developed a late infection, an overall wound infection rate of 13% (95% CI 7-19). Whilst this infection rate is higher than that previously reported from this unit using more prolonged (3 dose) antibiotic prophylaxis (9.8%, 95% CI 9.6-10) the difference is not likely to be significant because the patient groups were not matched, and the comparisons were sequential. On the basis of the present study it is concluded that 1 g of moxalactam disodium administered at the induction of anaesthesia in open colorectal surgery is inexpensive, is associated with a low incidence of side effects and its further use in colorectal surgery would seem to be justified.