The topographical position of the atypical epithelium replacing the lining of intramucosal gastric cysts was systematized in 88 Japanese resected stomachs having focal (elevated) neoplastic lesions. In the majority of lesions (87.5%) the atypical epithelium had replaced part of the luminal aspect of the cysts, suggesting that the replacement of the cysts by the atypical epithelium followed a downwards direction (i.e. towards the muscularis mucosa). Micrometric determinations indicated that the intramucosal cysts were larger beneath focal (elevated) neoplastic lesions than in the adjacent non-neoplastic gastric mucosa, suggesting that the cause (s) responsible for the retention of secretion had been present for a longer time in the former lesions. In some cysts, clusters of atypical cells or papillary formations with atypical cells were present at the narrowest part of the outlet from the glands, substantiating an obstructive-causal mechanism in those cysts.