To determine the need for prophylactic nasogastric decompression following laparotomy and the influence of cimetidine, 200 consecutive patients who underwent major abdominal procedures were prospectively randomized into one of four limbs: no tube-placebo; no tube-cimetidine; tube-placebo; and tube-cimetidine. Patients were evenly distributed among these groups with respect to age, sex, alcohol and tobacco use, previous operations, and types of operations. There was significantly longer time until passage of flatus, bowel movement, and cessation of intravenous fluids in the tube group (p less than 0.05). Duration of postoperative stay increased from 11.4 to 14.1 days in the intubated patients (p less than 0.05). There was also significantly more pain with and frequency of swallowing, and nose/throat discomfort in the tube group. Nasogastric tubes reduced the incidence of vomiting from 28 in the no-tube group to 10 in the tube group (p less than 0.05), but most had only one or two episodes. Cimetidine did not affect either the incidence of vomiting or the duration of intubation, but was associated with a significant increase in pneumonias (p less than 0.05). Five patients without tubes initially, and seven patients with tubes had to have them inserted or replaced for vomiting or abdominal distention, which occurred equally in the placebo and cimetidine limbs. There were no cases of aspiration pneumonia, gastric dilatation, or wound dehiscence in the trial, and the four anastomotic leaks were divided equally between the tube and no-tube groups. The results indicated that prophylactic decompression was unnecessary in most patients and associated with increased morbidity and delayed return of gastrointestinal function. Cimetidine lowered nasogastric output on the first postoperative day (p less than 0.05), but did not prevent vomiting.