The toxicity of organic-inorganic hybrid molecules appears to depend on the toxicity of the organic structure, the metals, and their interaction. However, very little is known about the structureactivity relationship of these molecules. In the present study, we investigated the cytotoxicity of triphenylstibane (Sb25) and its fluorine-substituted derivatives the triarylstibanes, using a culture system of bovine aortic endothelial cells. The results showed that the cytotoxicity of tris(4-fluorophenyl)stibane (Sb33) and tris(3,4,5-trifluorophenyl)stibane (Sb49) was higher than that of Sb25, suggesting that introduction of fluorine atoms into the benzene rings may potentiate the cytotoxicity of Sb25 in vascular endothelial cells. However, interestingly, tris(pentafluorophenyl)stibane (Sb35) was nontoxic. The pnictogen analogues tris(pentafluorophenyl)arsane (As35) and tris(pentafluorophenyl)phosphane (P35) showed a higher cytotoxicity than that of Sb35. In addition, the potentiation was much stronger with P35 than it was with As35. The intracellular accumulation of Sb35 was very low while the accumulation of As35 was higher than that of Sb25. These results collectively suggest that the hydrophobicity and metal of the organometallic compounds do not necessarily predict their cytotoxicity and intracellular accumulation in vascular endothelial cells.