Human umbilical vein endothelial cells were cultured in the presence of several oxygenated cholesterol derivatives that are known to affect the viability of other cell lines. 5-Cholestene-3 beta,7 beta-diol (7 beta-hydroxycholesterol) caused a time- and concentration-dependent perturbation of the endothelial cells. Exposure to 50 mumol/l of this compound for 18 hours resulted in marked contraction of the cells, followed by increasing cell detachment from the substrate and Trypan Blue uptake in detached cells. Concomitantly release of lactate dehydrogenase from the cells reached about 80% at 24 hours. The release of tissue plasminogen activator and tissue plasminogen activator inhibitor-1 antigens decreased at a concentration of 7 beta-hydroxycholesterol lower than that required for reducing general protein synthesis. 7 beta-Hydroxycholesterol at 50 mumol/l first increased the release and then (at 100 mumol/l) inhibited the synthesis of von Willebrand factor. Incubation with 100 mumol/l of 5-cholestene-3 beta, 7 alpha,22(R)-triol (7 alpha,22-dihydroxycholesterol)e and the isomeric 5-cholestene-3 beta, 7 beta, 22(R)-triol (7 beta, 22-dihydroxycholesterol) caused formation of intercellular gaps and some detachment of the cells after 24 hours. Cell injury was slightly more pronounced for the 7 alpha, 22-dihydroxycholesterol than for the 7 beta-isomer. Incubations with cholesterol under the same conditions gave no sign of cell injury.