It has been demonstrated that an increase in dietary calcium intake can lower the blood pressure of the hypertensives. We examined the effect of dietary calcium on blood pressure and vascular reactivity in DOCA-salt hypertensive rats. Blood pressure was significantly decreased after four weeks of calcium feeding. Nevertheless, the development of hypertension was not completely avoided. There was no difference between the calcium fed group and the control group in their response to NE, KCl and AVP in tail artery helical strips in normal calcium medium in vitro. However, the responses of these two groups to NE (10(-6) M) and AVP (10mU) were significantly different in Ca2+-free medium. Furthermore, the tail artery from Ca-fed group was less responsive to K+-induced relaxation. Since K+-induced relaxation has been applied to indicate the activity of Na+-K+ pump, we suggest that the activity of Na+-K+ pump may be involved and that the change in vascular reactivity to agonists might be rather insignificant in lowering the blood pressure of Ca-fed DOCA-salt hypertensive rats.