Two patients suffered duodenal rupture as a result of blunt trauma and developed gas gangrene of the peritoneal and retroperitoneal areas. Diagnosis of the rupture was delayed, as is often true in such cases. Both patients died despite antitoxin, large doses of antibiotics, and as much debridement as could be done within limits compatible with life. Both patients had undergone previous partial gastrectomy and vagotomy for duodenal ulcer. We suggest that the alterations in bacterial flora in the upper gastrointestinal tract attendant on gastrectomy and vagotomy may place patients with duodenal rupture at greater risk from gas gangrene than those with normal gastroduodenal segments.