Prostate cancer cell lines were treated with 1 μmol/L 3α-adiol, 1 μmol/L 3β-adiol or 10 nmol/L R1881. Cell cycle was assessed using the commercial Muse™ Cell Cycle assay kit. In VCaP and VCaPAA cells, 3a-, 3β-adiol significantly increased cell numbers in the G0/G1 phases, whereas cells in the S or G2/M phases were significantly reduced. R1881 showed an opposite effect with a reduced number of cells in the G0/G1 phases and increased number of cells in the S and G2/M phases. In VCapAA cells, no significant changes were detected (A–F). In LNCAP 3a- and 3β-adiol application led to increases in cells in the G0/G1 phases, whereas the number of cells in S and G2/M phases was significantly reduced. R1881 resulted in inconsistent changes (G–I) (n.s. = not significant, *P < 0.05, **P < 0.005, ***P < 0.0005).