The antiproliferative activity of previously synthesized (Z)-cholest-4-en-6-one oxime (1), (E)-cholest-4-en-6-one oxime (2), 7-aza-B-homocholest-4-en-6-one (3) and 6-aza-B-homocholest-4-en-7-one (4) and newly synthesized 6-thioxo-7-aza-B-homocholest-4-ene (5) and 6-aza-7-thioxo-B-homocholest-4-ene (6) was tested for their possible effects against two human tumor cell lines, cervical carcinoma (HeLa) and chronic myelogenous leukemia (K-562). Compounds 1-6, exerted a dose-dependent antiproliferative effect toward cell lines used in experimental design, showing high selectivity in their action for tumor cells in comparison to normal immunocompetent cells (non-stimulated PBMC and PHA-stimulated PBMC). Compounds 2, 3 and 4 exhibited a very high but selective antitumor activity, by inducing apoptosis in sensitive, for that purpose targeted tumor cell line (HeLa cells). Low toxic effect upon both non-stimulated, and PHA stimulated PBMCs from control, healthy volunteers, has been detected for compounds 1, 2, 3 and 4. The possible reasons for profound differences in the effects of this spectrum of steroidal compounds between tumor cell lines and normal stimulated and non-stimulated PBMCs are discussed. The molecular mechanisms for apoptotic events in HeLa cell line are suggested. The guidelines for further research are underlined.