The occurrence of different combinations of antral and corpus atrophic gastritis (AG) was studied in 127 sibs and 159 children of 73 gastric carcinoma patients. Seventy-three control probands, age- and sex-matched for the carcinoma probands, and their 379 first-degree relatives were used as controls. Sibs of gastric carcinoma patients revealed a significant enrichment of AG affecting simultaneously both antrum and corpus (combined AG), while no such enrichment could be demonstrated in children, who behaved on the whole similarly to the controls. In addition, sibs of gastric carcinoma patients showed a significant aggregation of combined AG also when compared with children of similar age. This suggests that genetic factors in addition to environmental ones participate in the accumulation of combined AG in sibs. The lack of phenotype AB in children excludes the possibility of dominant Mendelian inheritance, but leaves the possibility of a recessive autosomal or multigenetic inheritance. The enrichment of combined AG in sibs of gastric carcinoma patients could be one of the factors involved in the increased liability of close relatives of gastric carcinoma patients to contract gastric malignancy.