Finger skin circulatory responses to three forms of sympatho-adrenal activation were investigated in 14 patients with mild hypertension and 14 matched normotensive controls. Finger nailfold skin capillary blood cell velocity was measured by video-photometric capillaroscopy and finger pulse volume by strain-gauge plethysmography (digital arterial pulse amplitude; DAPA). DAPA decreased more markedly in the normotensive as compared with the hypertensive group during mental arithmetic stress (38 vs. 19%; P less than 0.05) and a cold pressor test (55 vs. 32%; P less than 0.05). Intravenous infusions of adrenaline (0.1-0.8 nmol/kg/min) decreased DAPA in normotensives but not in hypertensives (P less than 0.05). Capillary blood cell velocity was similar in the two groups at rest and decreased promptly and to a similar extent in both groups following mental arithmetic, adrenaline infusion and the cold pressor test (by approximately 60, 60 and 35%, respectively). It is concluded that mental stress and the cold pressor test induce instantaneous and marked effects on the skin circulation via neurogenic activation. The less marked effect on DAPA in the hypertensive group may reflect an elevation of basal vascular tone and/or early structural vascular changes in mild hypertension. The discrepancy between total finger and capillary circulatory responses to adrenaline may be attributable to different adrenoceptor populations and/or sensitivity in arteriovenous shunts, as compared with precapillary vessels.