This study investigated the antineoplasic potential of a new family of aminosteroids. The antiproliferative activity of seven 5α-androstane-3α,17β-diol derivatives selected from a screening study was measured on nine cancerous cell lines (HL-60, K-562, LNCaP, PC-3, Shionogi, MCF-7, MDA-MB-231, BT-20, and OVCAR-3) and two normal cell lines (peripheral blood lymphocytes and WI-38). The aminosteroids efficiently inhibited the cell growth of seven cancer cell lines [inhibitory concentration (IC(50)) values=0.2-6.4 µmol/l] and showed weak toxicity on normal cell lines. Two representative aminosteroids were tested and found to induce apoptosis and a G0/G1 cell cycle block in HL-60-treated cells, but not terminal myeloid differentiation. By a nuclear morphology analysis with fluorescence microscopy, typical apoptotic morphological changes were exhibited by treated cells. One aminosteroid tested in vivo (xenograft model) reduced the breast cancer (MCF-7 cells) tumor growth induced in nude mice. Furthermore, the information gathered suggests that this family of aminosteroids induced growth inhibition cells by arresting the cell cycle and triggering apoptosis.