The recently developed 13C-octanoic acid breath test allows the measurement of gastric emptying of solids. In this prospective study we wanted to investigate, whether the 13C-octanoic acid breath test using breath samples every half an hour is suitable in assessing gastric emptying in comparison to scintigraphy in diabetics. Furthermore, we examined the intraindividual reproducibility in healthy volunteers. 20 consecutive diabetics with clinical symptoms of gastroparesis received a solid double-labeled standard test meal. The meal consisted of 1 scrambled egg, labeled with 75 mg 13C-octanoic acid and 0.5 mCi 99mTc colloid, 50 g rye bread, 20 g butter, 200 ml orange juice; 280 kcal. Breath samples were taken at half hour intervals for 4 hours and analyzed for 13CO2 by isotope ratio mass spectrometry. Using a regression method gastric emptying half times (t 1/2) were determined and correlations to simultaneous 99mTc-scintigraphy were calculated. There was a moderate significant correlation of 13C-octanoic acid breath test t 1/2 and scintigraphic t 1/2 (R = 0.6; p = 0.008). The 13C-octanoic acid breath test t 1/2 obtained in 20 healthy volunteers measured at two separate days showed a coefficient of variation (VC), that was greater between subjects (VK = 42%) than between two measurements in the same subject (VK = 24%), which reflects a moderate intraindividual reproducibility. Taking breath samples every half an hour the 13C-octanoic acid breath test only reveals a moderate intraindividual reproducibility and a moderate correlation to scintigraphy in diabetics. For detailed assessment of solid gastric emptying in diabetics a 13C-octanoic acid breath test using shorter breath sampling intervals is recommended.