To see whether the increased peripheral vascular resistance seen in human hypertension is due to an altered reactivity of vascular smooth muscle, strips of digital arteries obtained post mortem from 13 hypertensive have been compared with those from 13 normotensives. The strips from the hypertensives were significantly thicker than those from the normotensives, as were those from male patients compared to females. This was reflected in a significantly greater response of the strips from the hypertensives and males to 80 mM KCl. The maximum responses to noradrenaline and 5-hydroxytryptamine, but not the concentrations required to produce 50% of the maximum responses, were significantly smaller in the strips from hypertensives than in those from normotensives. There were no significant differences between the strips from hypertensives and normotensives in either the maximum responses to angiotensin or barium chloride, or the concentration of those agonists required to produce 50% of the maximum response. It is concluded that the decreased reactivity to noradrenaline of the hypertensive vessels may be a sequel of either the increased pressure itself or increased exposure in vivo of the blood vessels from hypertensives to noradrenaline.