The 13C-octanoic acid breath test is considered a useful tool to measure gastric emptying both in physiological and pathological conditions. Many studies have concerned functional dyspepsia. Recently, breath test has been used in predicting a delayed gastric emptying in subsets of dyspeptic symptoms. In detail only postprandial fullness and vomiting are resulted significantly correlated with delayed solid emptying. Besides in the patients with dyspepsia and irritable bowel syndrome associated, intestinal disturbances did not seem to contribute to delay gastric emptying. In diabetic patients octanoate test has confirmed the percentages of delayed emptying obtained by means of scintigraphy. In other organic states (celiac disease, cirrhosis, renal failure, neurological disease, etc) most of reports have proved a delayed emptying of solids. In GERD and ulcer disease gastric function is resulted normal, being accelerated in distal gastrectomy and in hyperemesis gravidarum. From pathophysiological point of view Helicobacter pylori, extrinsic autonomic neuropathy (apart from diabetes) and autoimmunity do not seem to relate with gastric emptying, both in functional and organic disease.