The effects of massive small-bowel resection on antral gastrin tissue concentration and G-cell number have been investigated in the dog. Tissue gastrin concentrations increased significantly after resection from 16.8 +/- 2.6 ng/mg wet weight to 30.3 +/- 3.2 ng. Immunoreactive gastrin cell number also increased from 29.8 +/- 2.5 cell/mm2 to 43.1 +/- 3.0 cells/mm2. Immunocytochemistry demonstrated that the hyperplastic gastrin cells were found in small groups, with the majority of the immunoreactivity located at the luminal pole of the cells. This finding, linked to hypogastrinemia in the dogs after massive small bowel resection, suggests that some of the hyperplastic G cells may have an exocrine rather than endocrine function.