Three hundred and one first-degree relatives (series) of 73 gastric carcinoma patients and 358 control relatives (controls) of 73 computer-matched probands from a general population were studied by direct-vision gastric biopsy and functional and immunological examinations. The controls were representative of the series with respect to age, sex, birth and dwelling place, and relationship of the relatives. Series and controls behaved similarly as to total prevalence of gastritis, age and sex distribution of gastritis, serum gastrin level, and circulating gastric antibodies. On the other hand, the total prevalence of hyperplastic polyps, atrophic gastritis of the body and antrum, severe atrophic gastritis of the body, intestinal metaplasia, epithelial atypia, and achlorhydria was significantly higher in the series than in the controls. In subjects below 50 years of age the prevalence of severe atrophic gastritis of the body, intestinal metaplasia, and epithelial atypia was also significantly higher in the series. In addition, the mean age of the subjects with atrophic gastritis, intestinal metaplasia, epithelial atypia, and achlorhydria was lower in the series than in controls; however, significant differences were found only in female subjects with epithelial atypia and atrophic gastritis of the body. The results suggest that the prevalence of signs often considered premalignant is significantly higher in carcinoma relatives than in controls and that these signs show a trend to occur at an earlier age in carcinoma relatives. This could explain the significantly higher than expected death rate from gastric carcinoma in close relatives with this disease, found in the present and in other series.