This study tested the hypothesis that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] plays a role in human umbilical vein endothelial cells (HUVEC) cultures. HUVEC were incubated with 10 or 100 nM 1,25(OH)2D3 for 24 h, in the absence or presence of 40 ng/ml tumor necrosis factor-α (TNF-α) or 2 ng/ml interleukin-1α (IL-1α). 1,25(OH)2D3 did not affect HUVEC viability and proliferation, while TNF-α, alone or in combination with the hormone, significantly inhibited HUVEC viability. [3H]thymidine incorporation in HUVEC treated with TNF-α or IL-1α significantly decreased, in the absence or in the presence of the hormone, while the levels of vitamin D receptor markedly increased in the presence of 1,25(OH)2D3 alone or associated with TNF-α or IL-1α, in comparison to the control. The noteworthy increase in protein levels of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) induced by TNF-α was significantly decreased after incubation of the cells with 1,25(OH)2D3, this effect not being seen on E-selectin expression. Neither apoptosis nor nuclear translocation of NF-κB, induced in HUVEC by TNF-α was influenced by 1,25(OH)2D3 treatment.