The aim of the study was to evaluate what family characteristics and what morphological, functional and immunological changes of the gastric mucosa precede the development of gastric malignancy in a follow-up of 11-14 years. The material consisted of 301 first-degree relatives of gastric carcinoma patients, 183 relatives of pernicious anaemia patients, and of 358 control relatives of probands computer matched from the general population by age and sex for the carcinoma probands. All subjects were endoscopically examined in 1973-1976 and followed up to the end of 1987. According to cancer registry data, 11 cases of malignant gastric tumours (9 carcinomas, one carcinoid tumour and one anaplastic tumour with suspicion of Hodgkin's disease) had been diagnosed during the follow-up: 6 belonged to gastric carcinoma, 2 to pernicious anaemia and 3 to control families. The occurrence of malignancy was significantly related to the presence of advanced gastritis with atrophy and of intestinal metaplasia before the start of the follow-up. In relatives with achlorhydria and low serum pepsinogen I levels the incidence of malignancy did not significantly differ from that in controls of similar age and sex distribution. The risk of getting malignancy was about four-fold in female members of gastric carcinoma and pernicious anaemia families but was not increased in control families. The risk was increased only in female members and concerned only gastric malignancy being the expected one or even lower than the expected in regard to malignancies of other location.