The mean concentration of gastrin in serum was determined in healthy fasting persons (n = 27), it amounted to 56.8 pg/ml (SD = 19.8 PG/ML). The values of gastrin in serum of patients, who were grouped by endoscopicbioptic criteria of antral mucosa and who exceptionally showed diffuse inflammation of gastric mucosa, amounted to 73.2 pg/ml in patients with mild superficial gastritis (n = 24), to 73.4 pg/ml in those with severe superficial gastritis (n = 55), to 82.3 pg/ml in patients with chronic atrophic gastritis (n = 11) and to 70.7 pg/ml in those with chronic atrophic gastritis and intestinal metaplasia (n = 17). The concentration of serum gastrin in patients with additional pathological processes of gastric or duodenal mucosa was also determined. Patients with gastric resection according to Billroth II (n = 15) revealed gastrin values of 47.8 pg/ml, those with duodenal ulcer (n = 5) of 58.5 pg/ml, with gastric ulcer (n = 50) of 61.3 pg/ml, with polyps in stomach (n = 10) of 109.6 pg/ml and with neoplasms of the stomach (n = 27) of 77.7 pg/ml. Gastrin values were not correlated to age or sex. The difference between the mean gastrin concentrations of the mentioned groups of patients however is not marked enough and the range of values is too wide to characterize those groups by specific gastrin levels. The determination of gastrin in serum of fasting patients is not helpful for diagnosis of gastritis without antibodies to intrinsic factor or for diagnosis of certain localized pathological conditions in stomach or duodenum obviously.