The dietary intake of fluoride and the fluoride excretions in urine and stool were determined under controlled conditions in man. Fluoride balance studies have shown that the urinary fluoride corresponds to 50--60% of the intake, the fecal fluoride was very low, corresponding to 6% of the intake, and approximately 1 mg fluoride was retained per day during an average fluoride intake of 4.3 mg/day. The fluoride intake depended on the amount of fluoridated water consumed. The dietary fluoride content ranged from 1.2 to 1.5 mg/day. During the intake of supplemental fluoride the fluoride excretions increased but the ratio of the urinary/fecal fluoride was similar. Added fluoride is well retained. Following its discontinuation, very small amounts of the retained fluoride are excreted for several days. Inorganic elements, such as calcium, phosphorus, and magnesium, which have been shown to decrease the intestinal absorption of fluoride in animals were ineffective in man, while aluminum, given as aluminum-containing antacids, markedly decreased the intestinal absorption of fluoride and thereby decreased the retention of fluoride.