The introduction of cyclosporin A (CsA) is considered a cornerstone advance in immunosuppression. However, serious side effects such as hypertension have fostered an important body of research regarding their pathophysiology. Although the participation of several vasoactive factors in the hypertensive response has been described, recent attention has focused on endothelium-derived vasoactive factors, and several reports describe an overproduction of endothelin-1 and a deficient endothelium-dependent vasodilation. In the case of the latter, no definitive clues for the precise molecular mechanisms have been provided. We demonstrate that endothelial cells in culture synthesize more NO in the presence of CsA for 24 h in a concentration-response manner. This augmentation is correlated with a threefold increase in the endothelial constitutive NO synthase (ecNOS) transcript, which is time dependent and maximal at 24 h. The CsA-induced increase in ecNOS mRNA expression was blocked by actinomycin D but unaltered by cycloheximide. Levels of ecNOS protein were also enhanced by CsA after 24 h. These data establish that NO synthesis is moderately enhanced in endothelial cells exposed to CsA for long periods of time and describe a new mode of regulating ecNOS gene expression.