In 15 patients with uncomplicated gastric ulcers, basal and peak gastric acid outputs and fasting serum gastrin levels were studied before and after healing. The mean basal acid output [4.0 +/- 1.3 (SEM) mEq H+/hr], the mean peak acid output (29.5 +/- 5.1 mEq H+/hr), and the mean fasting serum gastrin level (80.3 +/- 16.7 pg/ml) in these patients did not change significantly with healing. Failure of gastric secretory function to change with healing suggests that mucosal resistance factors are more important than gastric acid secretion in the pathogenesis of a gastric ulcer.