In the fetal development of the mouse pancreas, endocrine cells have been found that express more than one hormone simultaneously. Our objective was to evaluate the existence of such cells in the human fetal pancreas. We found cells coexpressing two of the major pancreatic hormones (insulin, glucagon, and somatostatin) in sections of eight midgestational (12-18 weeks) pancreata and in 0-7% of cells in single-cell suspensions from midgestational pancreata. By electron microscopy, using granule morphology and immunoelectron microscopic techniques, we could confirm these findings and even detect cells containing three hormones. Morphologically different granules contained different immunoreactivities, suggesting parallel regulation of hormone production and packaging. In six newborn pancreata (born after 22-40 weeks of gestation), we could not find any multiple-hormone-containing cells. Subsequently, we evaluated whether multiple-hormone-containing cells proliferate by using pancreatic fragments and single-cell preparations at the light and electron microscopic level (six pancreata). No endocrine hormone-containing cells incorporated bromodeoxyuridine during a 1-hr culture period, indicating that these cells have lost the ability to proliferate under the conditions chosen. We conclude that, as in mice, the human fetal pancreas of 12-18 weeks of gestation contains endocrine cells that express multiple hormones simultaneously. These (multiple) hormone-containing cells do not seem to proliferate under basal conditions.