The purpose of this study was to evaluate the method of obtaining aspirated fluid for culture from the small intestine through a fiberoptic gastrointestinal endoscope for diagnosing small-bowel overgrowth. The study population consisted of 10 healthy volunteers and 26 patients with various gastrointestinal problems referred for routine endoscopic examination. The material to be cultured was obtained under direct visualization approximately 25 to 30 cm distal to the pylorus or from the afferent loop (in Billroth-II patients) with a sterilized sheathed wash pipe passed through the suction channel of the endoscope. Cultures were considered positive for bacterial overgrowth if total counts of organisms were 10(5)/ml or more. All healthy volunteers and 16 of 21 unoperated patients had sterile or insignificant growth, whereas all 5 patients who had Billroth-II operations had positive overgrowth. The endoscopic method for collection of proximal gastrointestinal fluid for culture is simple and can be performed during routine endoscopy.