In addition to the effects on tumor cell differentiation and growth inhibition, vitamin D3 derivatives may exert other cellular actions such as the inhibition of angiogenesis or the induction of apoptosis. In this study, we demonstrated that vitamin D3 derivatives, 1,25-dihydroxyvitamin D3, the natural derivative and Ro 23-7553, a synthetic derivative, displayed complex effects in tumoral colonic HT 29 cells. Indeed, as a function of the stage of culture, they induced either apoptosis or differentiation along with a constant cell cycle blockade in G1. Intracellular calcium analysis indicated that treatment resulted in disturbance in the distribution of calcium suggesting a possible role for intracellular calcium in the observed effects. The association of 9-cis-retinoic acid, the ligand of RXR, with vitamin D3 derivatives modified the demonstrated effects, indicating in our model, a preferential effect of vitamin D3 derivatives via the heterodimeric form of the receptor.