Young rats were maintained on 2 diets containing 14.2 and 1.2 g calcium/kg food, respectively. Each group was divided into 3 subgroups whose diets were supplemented with fluoride, vitamin D2, or both. Rats on low-calcium diets supplemented with fluoride decreased their food intake and the gain in body weight was smaller. The addition of vitamin D resulted in a body weight increase. The level of fluoride in the soft tissues of the rats kept on low-calcium diets was 2–3 times that of the corresponding tissues of the rats kept on high-calcium diets. The percent of retention of fluoride by low-calcium fed groups was 2–3 times the amount of fluoride than that of the high-calcium diet rats. Vitamin D increases fluoride retention irrespective of the calcium content of the diet. In the rats on the high-calcium diet, the effect of fluoride on weight gain is not significant.