Transforming growth factor-betas are members of a superfamily of multifunctional cytokines regulating cell growth and differentiation. Their functions in neural and endocrine cells are not well understood. We show here that transforming growth factor-betas are synthesized, stored and released by the neuroendocrine chromaffin cells, which also express the transforming growth factor-beta receptor type II. In contrast to the developmentally related sympathetic neurons, chromaffin cells continue to proliferate throughout postnatal life. Using 5-bromo-2'-deoxyuridine pulse labeling and tyrosine hydroxylase immunocytochemistry as a marker for young postnatal rat chromaffin cells, we show that treatment with fibroblast growth factor-2 (1 nM) and insulin-like growth factor-II (10 nM) increased the fraction of 5-bromo-2'-deoxyuridine-labeled nuclei from 1% to about 40% of the cells in the absence of serum. In the presence of fibroblast growth factor-2 and insulin-like growth factor-II, transforming growth factor-beta1 (0.08 nM) reduced 5-bromo-2'-deoxyuridine labeling by about 50%, without interfering with chromaffin cell survival or death. Doses lower and higher than 0.08 nM were less effective. Similar effects were seen with transforming growth factor-beta3. In contrast to transforming growth factor-beta, ciliary neurotrophic factor, which inhibits proliferation of sympathetic progenitor cells, was not effective on rat chromaffin cells from postnatal day 6. Glucocorticoids also suppress DNA synthesis in fibroblast growth factor-2/insulin-like growth factor-II-treated chromaffin cells. This effect was not mediated by chromaffin cell-derived transforming growth factor-beta, as shown by addition of neutralizing antibodies. We conclude that one function of adrenal medullary transforming growth factor-beta may be to act as a negative regulator of chromaffin cell division.