76 patients were examined for duodenogastric reflux by gastroscopy and by a non-invasive isotope method using Tc-99m diethyliminodiacetic acid. The bile acid concentration of endoscopically aspirated gastric juice was measured. The patients with endoscopically diagnosed bile in the stomach (51 patients) had duodenogastric reflux significantly (p less than 0.05) more often in the isotope examination than the patients without bile observed in the stomach (25 patients). The amount of bile as estimated endoscopically correlated well with the bile and acid concentration of gastric juice. However, 18 patients with endoscopic bile reflux had no reflux in the isotope examination and 9 patients without endoscopic bile reflux had a mild reflux isotopically. The reflux estimations made endoscopically tend to give comparable results in general, but in many patients the results entirely differ from those obtained with the isotope method. We suggest that this difference is mainly due to the invasive nature of the endoscopic examination.