The effect of fluoride on bone metabolism was studied using Japanese quail fed diets containing 1.2% calcium, 1.2% calcium + 0.075% fluoride, 0.4% calcium, and 0.4% calcium + 0.075% fluoride. In the first experiments, quail were fed the diets immediately after hatching. Low calcium intake (0.4%) resulted in a 23% reduction in body weight, a 38% decrease in bone ash and a twofold elevation in bone pyrophosphatase levels compared with controls (1.2% calcium) after 11 days of treatment. Supplementation of fluoride to the low calcium diet, however, resulted in increased calcium retention, growth rates, and bone ash. The bone calcium/phosphorus ratio did not vary significantly and did not appear to be affected by the experimental diets. An elevation of bone magnesium, however, was observed in both of the fluoride-supplemented groups as well as the low calcium group compared with the control. In further experiments, groups of quail were fed the control diet (1.2% calcium) for 10 days and then one of the other diets for the following 35 clays. Under these conditions, the birds fed the diet containing only 0.4% calcium did not develop any severe calcium deficiency signs and for the most part appeared normal. Tetracycline labeling studies indicated a significant increase in periosteal bone formation in the fluoride-supplemented groups. Von Kossastained bone sections indicated adequate mineralization of this new bone. An increase in the number of osteons appeared to be present in bone sections from fluoride-treated birds. These changes in bone, however, were not accompanied by an increase in bone strength. Dietary fluoride supplementation resulted in a 30% decrease in bone torsional strength. The results demonstrate that fluoride supplementation increases calcium retention, but at a high level has little effect on bone integrity and strength.