In vitro models of human prostatic carcinogenesis are increasingly available and include representatives of normal, immortal, tumorigenic and metastatic phenotypes. In this study, growth regulation of immortal, but non-tumorigenic, human papillomavirus-transformed prostatic epithelial cells was compared to that of their tumorigenic variants. These variants were created either by exposure to a carcinogen or by passage through mice. In all cases, tumorigenic cells retained responsiveness to a potent mitogen, epidermal growth factor, and to a potent growth inhibitory factor, 1,25-dihydroxyvitamin D3. Responses to other growth regulatory factors were altered. One set of transformants, CA-HPV-10 and its tumorigenic variants 5019 and 5019IIc, lost their requirement for insulin-like growth factor. Another set, RWPE-1 and its tumorigenic variant 129Nu5002-1 Tu, became unresponsive to growth inhibition by transforming growth factor-beta. The only alteration uniquely correlated with the tumorigenic phenotype was loss of response to retinoic acid. This factor, which inhibits growth of normal and immortal but non-tumorigenic prostatic epithelial cells, had no effect on tumorigenic 129Nu5002-1 Tu cells. We previously reported that conversion of an SV40-immortalized prostatic epithelial cell line to tumorigenicity by introduction of the ras oncogene also resulted in loss of responsiveness to growth inhibitory activity of retinoic acid. 129Nu5002-1 Tu cells, which do not have an altered ras gene, gained the same phenotype. This suggests that loss of inhibition by retinoic acid may be a critical element in the tumorigenic conversion of prostatic epithelial cells.