To evaluate the involvement of the apoptosis-suppressing protein BCL-2 in the gastrin-dependent mechanism of induction of gastric enterochromaffin-like (ECL) cell carcinoids, the endocrine cell of the oxyntic mucosa were immunohistochemically investigated in (a) 10 normogastrinemic subjects with histologically normal gastric mucosa; (b) 22 patients with endocrine cell hyperplasia and affected by hypergastrinemic conditions with different risk of gastric carcinoid development, such as sporadic Zollinger-Ellison syndrome (sZES; n = 9), ZES associated with multiple endocrine neoplasia-1 (MEN-1; n = 4), and atrophic fundal gastritis (AFG; n = 9); (c) 14 patients with ECL gastric carcinoids accounting for a total of 31 tumors investigated. In the normal oxyntic mucosa, BCL-2 was consistently expressed by a subset of endocrine cells accounting for 50.0% (median; range, 24.6-74.0%) of the total number of endocrine cells immunostained for chromogranin A (CgA) in consecutive sections. BCL-2 immunoreactive cells were located mostly in the middle mucosal layer, suggesting a role for the protein during downward migration of maturing endocrine cells. No BCL-2 immunoreactivity was found in other specialized gastric epithelial cells. Expression of BCL-2 by hyperplastic oxyntic endocrine cells (mostly ECL cells) varied in parallel with the risk of carcinoid development. In fact, the ratio of BCL-2- to CgA-immunoreactive cells was reduced (median, 4.6%; p less than 0.0001; range, 0.9-42.0%) in sZES, a condition showing virtually no risk, unchanged (median, 55.6%; range 29.4-83.8 %) in cases of MEN-1/ZES with intermediate risk, and increased (median 87.6%; p less than 0.014; range, 48.8-199.4%) in cases of AFG, a condition at the highest risk of carcinoid. In ECL cell carcinoids, BCL-2 expression varied markedly from one tumor to another even in the same patient and was low or absent in most cases. In both hyperplastic and neoplastic ECL cells, an inverse relation between BCL-2 expression and CgA immunoreactivity, that is, the cell granule content, was found. These results suggest that BCL-2 expression by hyperplastic ECL cells is independent of the influence of serum gastrin and may contribute to the development of ECL cell carcinoid tumors by extending cell exposure to oncogenic factors. Once a carcinoid tumor is established, BCL-2 expression becomes inconsistent.