The aim of this study was to assess the influence of the physiological changes of gastric emptying on the simplified 14C-urea breath test. Thirty patients performed the test in fasting conditions. Patients were orally administered 0.074 mega Bq of 14C-urea, mixed with 0.0185 mega Bq of 99mTc-S colloids in 25 ml water. A breath sample was taken before and 10 min after intake of the tracers and followed by a 2 min planar anterior scintigraphic image of the abdomen to measure gastric activity. Gastric emptying was estimated by dividing the residual gastric activity at 10 min by the total activity in the abdomen. The procedure was performed twice for each patient after a 24 h interval. The repeatability of both the gastric emptying test and the urea breath test was assessed by the method described by Bland and Altman. The coefficient of repeatability of the urea breath test was 1.18 for a confidence interval of 95%. The coefficient of repeatability of gastric emptying was 27.4. There was no significant correlation (r= 0.08) between the plot of the individual modifications of urea breath test and residual gastric activity in two successive tests. It is concluded that the physiological changes of gastric emptying do not influence the results obtained by the simplified, single-sample 14C-urea breath test.