The effects of KCI continus tablet(K-Contin(R)) on the serum level of K and uric acid during hydrochlorothizide therapy(25mg/day) were evaluated in 30 patients with essential hypertensien. The results are as follows : 1) During hydrochlorothiazide therapy(25mg/day), 23% of all patients showed hypopotassemia(<3.5mEq/1) while no patient developed hypopotassemia after potassium supplement therapy(8 mEq/day). 2) During the period of K supplement, the level of serum uric acid showed less elevation. 3) The side reaction of KCI continus tablet were mild indigestion which developed in two patients and disappeared soon without any particular treatment. In conclusion, the KCI continus tablet is useful in the prevention of hypopotassemia during chronic diuretic therapy.