The bioavailability of potassium (K) from orally administered 10 per cent potassium chloride (KCI) solution has been compared with that from a slow‐release KCl tablet (Slow‐K) in 10 normal subiects under metabolic balance conditions. After a single 40 mEq. KCl dose, urinary K increased sooner and to greater peak levels after the solution was administered. In both cases greater amounts of K appeared in the urine when administered in the fasting than in the postprandial state. In 4 days of administration there was no difference in the net increment in urine K produced by equivalent doses of either preparation. No significant toxicity was experienced with either preparation. The unpleasant taste of the KCI solution was noted by each subject.