In 37 patients with hypertension and/or renal disease, blood from a peripheral and a renal vein was drawn during renal vein catheterization. The serum gastrin concentrations were determined and found by paired comparison to be statistically significantly (p less than 0.05) higher in the peripheral than in the renal vein. A test meal was given to 9 male controls and 7 male azotemic patients, and the serum gastrin concentration response determined. The mean fasting serum gastrin values were 173 +/- 22 pg/ml in the group of patients versus 42 +/- 5.5 pg/ml in the controls. The serum gastrin response was significantly higher and of longer duration in the azotemic patients than in the controls. The pentagastrin-stimulated gastric acid secretion was, however, equal in the two groups.