Vascular smooth muscle strips were examined during the development of hypertension in rats treated with deoxycorticosterone acetate (DOCA) plus saline to determine if the changes in the contractile responses precede or succeed the increase in blood pressure. After treatment with DOCA/salt for 1, 3 and 4 weeks, aortic and portal vein strips were prepared from control and treated rats for studies of cumulative dose-response relationships to noradrenaline (NA) in Krebs' solutions containing normal (2.5 mM) or low (0.2 and 0.4 mM) concentrations of Ca. 1 week of treatment did not result in any change in blood pressure or in the stress (force/area) developed by the aortic strips in response to NA in normal or low Ca. 3 weeks of treatment caused a significant increase of pressure and the aortic strips developed a significant decrease of stress in response to NA in normal, but not in low Ca. 4 weeks of treatment resulted in a significant increase of pressure and a significant decrease of stress in response to NA in low, as well as in normal, Ca. In contrast to the aortic strips, there was no change in the force induced by NA in the portal vein strips at any time. Thus, the decrease of contractile response in the aortic strips during treatment with DOCA/salt followed the same time course as the increase of arterial pressure and may be a consequence of high blood pressure.