Flow cytometric measurements of cellular DNA have been performed on biopsy specimens obtained by gastroscopy in patients with normal gastric mucosa (controls), superficial and atrophic gastritis, and resected stomachs. Aneuploidy was found in two biopsy specimens from a patient with superficial gastritis and in one specimen from a resected stomach. The fractional number of cells with a DNA content corresponding to the DNA synthetic and (G2 + M) phases of the cell cycle was defined as the 'proliferative index' (PI). No difference between the antral and body part of the stomach was found for the PI in controls or between controls and superficial and atrophic gastritis. PI was weakly but significantly correlated to a selection of mucosal enzymes. In resected stomachs increased PI was found when compared with that in the body part of the stomach in controls (p less than 0.01). Biopsy specimens with intestinal metaplasia (p less than 0.01) or atrophy (p less than 0.05) in the resected stomach showed significantly higher PI when compared with specimens with such findings from the body part of the stomach in atrophic gastritis.