A series of 127 consecutive patients with symptoms and signs and radiological features suggestive of acute small bowel obstruction underwent water-soluble contrast small bowel follow-through examination. A dose of 100 ml of Gastrograffin in adults, or 20-50 ml in children, was injected via a nasogastric tube and supine plain abdominal radiographs were taken at 30 min and 4 h after administration. If contrast passed to the colon a non-operative course was followed. If there was a clear cut-off in contrast level in the small bowel or if contrast failed to pass into the large bowel by 4 h, patients underwent laparotomy. Based on these radiological findings 15 patients (11.8%) underwent surgery and all had established small bowel obstruction at laparotomy. The remaining 112 patients were successfully managed conservatively. Water-soluble contrast radiology is safe, easy to use and to interpret, and is a major benefit in differentiating mechanical from other causes of small bowel obstruction. Our experience indicates that this underused technique is of significant value in identifying those patients who require urgent surgery.