Androgen signaling is crucial for the growth and development, as well as for tumorigenesis of the prostate. However, many of the prostate epithelial cell lines developed previously, either normal or tumorigenic, do not express androgen receptor (AR) or respond to androgen. In order to advance our understanding on how androgen signaling regulates the growth and the differentiation status, and affects tumorigenicity of the epithelial cell, we performed experiments on HPr-1, a prostate cell line recently immortalized from normal human prostate epithelial cells. In the present study, AR was stably transfected into HPr-1 cells by replication-defective retrovirus. Treatment of HPr-1AR cells with androgen resulted in cell differentiation and growth retardation accompanied with up-regulation of cytokeratins K8 and K18, prostate specific antigen, p21 and p27, and down-regulation of c-myc, bcl-2 and telomerase activity. Our results suggest that androgen promotes the process of differentiation in a human papillomavirus 16 E6/E7 immortalized prostate epithelial cell line which may reflect the normal effects of androgen on prostate cells.