© 2018 Comenius University.OBJECTIVES: Nigella sativa oil and thymoquinone were comparatively tested in vitro for their effects on human cancer cell lines (glioma,T98; prostate, LnCaP) as well as mouse embryonic fibroblast cell lines (3T3), and for the induction of apoptosis. METHODS: Individual cell lines were treated with thymoquinone and N. sativa oil for 24 and 48 hr. Survival rate with MTT, apoptosis with fl ow cytometry and caspase-9 mRNA enzyme levels with RT-PCR were determined in vitro. RESULTS: Application of respective concentrations of N. sativa oil (excluding 100 μg/mL for 48 hr) did not change the number of tested cell lines, however, treatment with thymoquinone reduced the number of all cells significantly. Thymoquinone also exerted its apoptosis inducing effect through the activation of caspase-9. CONCLUSION: Differing with the type of cancer cells, thymoquinone posseses a strong contentration and time dependent survival reducing effect on cancer cells via apoptosis.