Fluorosis is characterized by hypermineralization. Kinetics of calcium metabolism was determined in three subjects with skeletal fluorosis using radioactive Ca45. The subjects who were on a constant intake of calcium (800 mg./day) were administered Ca45 (0.1 μc./Kg.). Calcium and Ca45 radioactivity in serum, urine and feces were determined during the next 10 days. These patients showed a high retention of dietary calcium and Ca45 radioactivity. An estimate of exchangeable pool of calcium and bone formation rate obtained from Ca45 specific activities of serum and urine indicated that these parameters of calcium kinetics were much elevated in these subjects.