The lumen of gastrostomy tubes is frequently colonized with Candida. To investigate the source of this contamination, 20 consecutive malnourished patients undergoing placement of a percutaneous endoscopic gastrostomy tube and ten ambulatory controls having routine upper endoscopy performed had both their oral cavity and gastric antrum swabbed and cultured. Percutaneous endoscopic gastrostomy tube recipients who after several weeks were still under our care (9 of 20) had the lumen of their tubes cultured. Fungi were isolated from the stomach in 13 (65%) of 20 patients undergoing percutaneous endoscopic gastrostomy tube placement but in only 1 of 10 ambulatory patients (p < .01). The species isolated from the oral cavity, the stomach, and later the gastrostomy tube were identical in most cases. We conclude that gastrostomy tubes are probably colonized by oral organisms that have made their way into the stomach.