The prostate gland is dependent on androgens for the maintenance of its normal growth and functional integrity. Initially, growth of the majority of prostate tumours can be manipulated by endocrine therapy. In the present study, we evaluated the effects of sex steroids on the cell growth and expression of the C-myc oncogene in two human prostatic adenocarcinoma cell lines. We found that dihydrotestosterone increases the proliferation rate of prostatic cells, and amplification of C-myc oncogene is hormone-dependent. We also demonstrated a positive correlation between the number of cells positive for C-myc oncogene and oncoprotein in hormone-treated prostated cell lines.