A retrospective study of 50 patients with infantile hypertrophic pyloric stenosis (IHPS) showed wound infection in six patients. In an attempt to assess the value of antibiotic prophylaxis in infantile pyloromyotomy 150 patients with infantile hypertrophic pyloric stenosis were entered in a prospective randomized controlled study. The infants were allocated to receive a dose of Cefuroxime (30 mg/kg) at induction of anaesthesia or no antibiotic. Eight infants developed wound infection, five in the control group and three in the antibiotic prophylaxis group. Although the difference between the two groups was not statistically significant there was an overall reduction of wound infection (6.5%) compared with pre-trial figures (12%). In order to study the bacterial flora in the umbilicus in these infants, culture swabs were taken from the umbilicus on admission, immediately prior to surgery and from the wound prior to skin closure. It was shown that the umbilicus was not the source of infection.