Previously, we found that transforming growth factor beta (TGF-beta) inhibits proliferation of normal human ovarian epithelial cells. In addition, although only 1 of 5 immortalized ovarian cancer cell lines was inhibited, TGF-beta inhibited proliferation of 19 of 20 primary epithelial ovarian cancers. In this study, we examined whether TGF-beta induces apoptosis in normal and malignant ovarian epithelial cells. Among 5 immortalized cell lines, only OVCA 420 is markedly growth inhibited by TGF-beta, and this was the only cell line in which TGF-beta elicited DNA fragmentation characteristic of apoptosis. Induction of apoptosis in OVCA 420 was time and concentration dependent and could be partially inhibited by concurrent treatment with an anti-TGF-beta mAb. Although apoptosis was not seen in normal ovarian epithelial cells (n = 7), [3H]thymidine incorporation was inhibited in all cases [mean = 61.2 +/- 7.2% (SD) of untreated control; P < 0.01]. Similarly, TGF-beta inhibited [3H]thymidine incorporation in all 10 primary ovarian cancers (mean = 40.4 +/- 7.1% of control; P < 0.01), but only 3 of 10 (30%) were found to undergo apoptosis when treated with TGF-beta. There was no relationship between p53 status of the ovarian cancers and the ability of TGF-beta to elicit apoptosis. In conclusion, TGF-beta inhibits proliferation but does not induce apoptosis in normal human ovarian epithelial cells. In contrast, some ovarian cancers that are growth inhibited by TGF-beta also undergo apoptosis. These data are consistent with the hypothesis that malignant cells are more susceptible to apoptosis than their normal nontransformed counterparts.