1. The present study investigated whether rapid desensitization (tachyphylaxis) develops after exposure of human hand veins to angiotensin (Ang)II and whether pretreatment with indomethacin affects its development. 2. Venoconstrictor responses to increasing (2-256 ng/min) and constant (50 ng/min) doses of AngII and noradrenaline (NA) infusion were obtained in six healthy male subjects using the dorsal hand vein technique. After pretreatment with indomethacin and placebo, venoconstrictor responses to 50 ng/min AngII infusion were obtained in eight healthy male subjects. 3. The maximal mean (+/- SD) venoconstrictor response to NA (obtained with 256 ng/min NA) was 93.1 +/- 4.7%, whereas that to AngII (obtained with doses between 16 and 128 ng/min) was 43.8 +/- 12.2%. Continuous infusion of NA induced constant venoconstriction, whereas the venoconstrictor response to AngII peaked 3 min after the beginning of infusion and, thereafter, was attenuated. 4. Venoconstriction in response to constant AngII infusion after indomethacin pretreatment was significantly larger than that after placebo from 6 to 18 min after the initiation of infusion. 5. These findings show that rapid desensitization to AngII develops in human hand veins and this is compatible with the hypothesis that vasodilator prostaglandins are involved in the development of this desensitization.