Evidence for a common endodermal stem cell has been derived from kinetic studies in mouse small intestine which indicate that the turnover characteristics of endocrine cells are similar to those of other cell lineages (columnar and goblet cells). We have used continuous tritiated thymidine labelling and peptide immunocytochemistry on resin embedded semithin sections, a combination of techniques which have not been used before in the small intestine. Our data show that the turnover time for endocrine cells in the small intestine is 10 days, considerably longer than the four days suggested by previous studies, although for columnar and mucous cell lineages, turnover rates are similar to the published literature. In the stomach, the turnover time was very slow indeed (of the order of 45-60 days). These results show that endocrine cells do not share turnover characteristics with the other cell types and suggest that they constitute a kinetically distinct cell population independent of the other cell lineages. These data are not consistent with a common stem cell origin for gut endocrine cells.