Fluoride balances were determined in healthy adult males under metabolic ward conditions. This is the first fluoride study to use the diffusion method in exploring the balances of subjects ingesting basal (i.e., everyday) diets with deionized water for cooking and drinking. Certain groups were given daily supplements of 5 or 10 mg. fluoride as sodium fluoride in divided doses with meals. Fluoride was measured in the diets, sodium fluoride tablets, urine, feces, and serum. Approximately 90% of the fluoride excreted was found in the urine and the remainder in the feces in all groups. In the control subjects, fluoride balances were uniformly negative (mean of -0.40 mg/day); in contrast, balances were uniformly positive (mean of +1.38 and +2.88 mg/day, respectively) in subjects receiving 5 or 10 mg F supplements daily. Serum ionic fluoride concentration increased proportionally to fluoride intake and averaged 0.016, 0.029, and 0.040 ppm in the control, 5-mg and 10-mg groups, respectively. These fluoride supplements did not cause any clinical or laboratory abnormality in any subjects.