Recent studies have demonstrated oestrogen receptors in tissues other than those considered to be sex hormone responsive, for instance in gastric cancer. In vitro experiments have shown oestradiol to be trophic to gastric cancer cell lines. The effect of D5 (an oestrogen receptor-related protein) status on survival was therefore studied in a group of 188 consecutive patients undergoing surgery for gastric cancer. Ninety-two patients (49 per cent) were positive for the D5 antibody. There were no differences between the D5-positive and D5-negative groups for age or adverse prognostic features such as high grade tumours or advanced stage. The D5-negative patients had a significant survival advantage over the D5-positive patients. The 95 per cent confidence interval for survival in the patients with D5-negative tumours was 63-101 weeks compared with 39-66 weeks for the patients with D5-positive tumours (Mantel-Cox statistic = 4.15, P = 0.042). Prognostic factor analysis with a Cox proportional hazards model showed tumour stage (P = 0.001) and D5 status (P = 0.003) to be significant independent factors in gastric cancer. Laurén type, grade and gender were not significant independent factors in this small series.