There is a constancy of plasma fluoride content of individuals who use communal water within the range 0.15– 2.5 ppm fluoride. With an intake of 5.4 ppm of fluoride in the communal water there is a slight but significant elevation of the plasma concentration. There is no evidence of a marked or prolonged rise of plasma fluoride content following the ingestion of 1.0 mg fluoride or of a diurnal variation of plasma fluoride content. The mean plasma fluoride concentration of hospitalized patients is not different from that of normal people. The factors relating skeletal fluoride content to small and short-term rises of plasma fluoride concentration are discussed. Submitted on November 19, 1959