The acute hemodynamic effect of cyclosporine in man is controversial. A randomized, double blind, placebo-controlled, cross-over study was undertaken to evaluate the effect of a single oral dose of cyclosporine (20 mg/kg body weight) on mean blood pressure (MBP), heart rate (HR), forearm blood flow (FBF), and vascular resistance (FVR) in 16 healthy adult subjects. Subjects were studied twice, with an intervening period of 2 weeks, before and after the administration of either cyclosporine or the vehicle olive oil. Blood pressure was measured on brachial and digital arteries. After 30 min of rest, basal measurements were obtained and individuals were randomly assigned to receive either cyclosporine or the vehicle, and the same measurements were repeated 2 h later. Mean whole blood levels of cyclosporine were 1542+/-387 ng/mL (range 1000 to 2550) 2 h after the administration of a single oral dose of cyclosporine. Cyclosporine did not cause any significant change in the hemodynamic parameters when compared with vehicle. Pre- and post-cyclosporine data were as follows (means +/-/SD): MBP (determined by Finapres on the digital artery), 92+/-10 v 95+/-11 mm Hg; HR, 66+/-10 v 68+/-11 beats/min; FBF, 3.90+/-1.3 v 3.8+/-1.8 mL/ 100 mL/min; and FVR, 28+/-9 v 33 +/-18 units, respectively. For the vehicle the results were: MBP, 94+/-9 v 94+/-9; HR, 67+/-9v 67 /-11; FBF, 3.3+/-1.6 v 3.2+/-2.0; FVR, 35+/-14 v 37+/-15, respectively. These figures did not differ from those obtained with the auscultatory method applied to the brachial artery among 10 selected subjects studied with Finapres. In conclusion, we found no evidence that at supratherapeutic doses cyclosporine causes acute increase in blood pressure or peripheral vasoconstriction in humans.