It has long been suspected that sodium and potassium intake influence blood pressure. Since both these electrolytes can be modified by diet, attention has focused on decreasing sodium intake and increasing potassium intake as a potential way of treating and preventing hypertension. Several short-term controlled clinical trials have examined the effect of supplemental potassium intake on blood pressure, but with inconsistent results. The Minnesota Mount Sinai Hypertension Trial (MSHT) is a double-blind study comparing placebo with potassium supplementation for controlling blood pressure in hypertensive men on a sodium-restricted diet over a 2-3 year follow-up period. At the time of randomization to placebo or supplemental potassium and through 12 weeks of follow-up, the patients were taking antihypertensive medication. This preliminary report compares blood pressure changes between the placebo and supplemental potassium groups over the first 12 weeks of the trial.