The incidence and prevalence of intestinal metaplasia (IM) of three types were investigated in 1,041 endoscopic biopsy specimens collected from patients with gastric abnormalities in 1981 and 1982. Intestinal metaplasia was classified as type I (complete), type II (incomplete, sulfomucin-negative), or type III (incomplete, sulfomucin-positive). Intestinal metaplasia, found in 244 biopsy specimens (23%), was prevalent in gastric carcinoma (65%), compared with the incidence of 18.4 per cent in benign conditions. The sulfomucin-negative types I and II were more common than type III and were present in both benign conditions (98 per cent) and carcinoma (64 per cent). In contrast, type III IM was seen in only 12 per cent of IM-positive biopsy specimens, 90 per cent of which (26 of 29) were from patients with carcinoma. The high specificity of type III IM (98 per cent) might be acceptable for screening purposes, but its sensitivity of 36 per cent for gastric carcinoma is low. Two main factors would seem to account for the low sensitivity, as shown in the comparative analysis of IM types in gastrectomy specimens and the previous biopsy specimens from 93 patients: 1) sampling and 2) the association of type III IM with gastric carcinoma of the intestinal type but not with diffuse gastric carcinoma. The data thus confirm a significant relation between incomplete sulfomucin-secreting IM (type III) and gastric carcinoma of the intestinal type (P less than 0.001). This variant of IM should be considered a risk factor, and its presence in a biopsy specimen should prompt close surveillance.