Basal and pentagastrin-stimulated peak acid outputs were determined in 21 subjects with chronic atrophic gastritis and 10 subjects with chronic superficial gastritis. All subjects were Caucasian. The histological diagnosis was based on multiple gastric biopsy specimens obtained through a fibregastroscope. Comparison of the results with those of a previously reported Caucasian control group show that the mean basal acid outputs of subjects with chronic (superficial) gastritis were significantly higher than that of controls and subjects with chronic atrophic gastritis. No significant difference was found in the mean peak acid outputs of controls and subjects with chronic atrophic gastritis or chronic (superficial) gastritis.