1. In the isolated rabbit arteries, the effects of intravenous cyclosporin A preparation (Sandimmun) and its solvent (Cremophor-EL) on acetylcholine-induced endothelium-dependent relaxation were investigated in the absence and presence of indomethacin (10 - 5 M), a cyclooxygenase inhibitor.2. The effect of indomethacin on the drug- and solvent-induced contraction of superior mesenteric artery was also evaluated.3. The inhibitory effects of cyclosporin and the solvent on endothelium-depenent relaxations were decreased by indomethacin. The direct contractions produced by the drug and the solvent in rabbit mesenteric artery were inhibited by indomethacin.