The influence of salt restriction for 3 months on blood pressure, peripheral vascular resistance (observed by occlusive plethysmography), erythrocyte sodium, platelet calcium, and pH, was studied in eight untreated essential hypertensive patients. A low salt diet decreases blood pressure, vascular resistances, erythrocyte sodium, and platelet calcium, but not platelet pH. A strong positive correlation was noted between baseline platelet calcium and vascular resistances (r = 0.95, P less than .01). But during the salt restriction period, a negative correlation has been observed between the changes in these parameters, which casts doubt on the use of the platelet as a model of the smooth muscle cell.