Prostate cancer is a major medical problem that is expected to affect over 300,000 American men and cause over 40,000 deaths in 1997. Despite its widespread prevalence and because of the difficulties in clinical diagnosis and treatment of the disease, the etiological mechanism underlying prostate carcinogenesis remains poorly understood. Elucidation of the mechanism of prostate tumorigenesis has been slowed by a lack of tumor tissues and the limited number of human cell lines available for study. In vitro human cell models to study the molecular biology of prostate cancer progression are urgently needed. Normal human prostate cells require immortalization to provide a practical system for transformation studies. Neoplastic transformation of human prostate epithelial cells in culture has been achieved recently in a stepwise fashion--immortalization of primary cells in culture and conversion of the immortalized cells to a tumorigenic state. Reviewed here are the steps involved in the neoplastic transformation of human prostate cells. To provide an insight into the molecular and genetic mechanisms involved in the conversion of normal cells to a neoplastic state of growth, the authors have attempted to put into perspective the history of human prostate epithelial cell transformation by a combination of carcinogenic agents, and to discuss the current state-of-the-art in transformation of human prostate epithelial cells in culture.