Summary A group of rats were placed on a high fluoride diet for 28 days. Portions of their scapulae were then removed and devitalized, and in the meantime the animals were put on a diet of normal F content. A control group of animals were similarly treated, but did not get a high F diet. The scapulae were implanted subcutaneously into the respective donor animals and removed after 2 or 4 weeks, and examined histologi-cally and chemically. Despite an F content 7 to 10 times higher in the experimental compared to the control animals'scapulae, the tissue responses were identical: a fibrous capsule formed around the implants and giant cells appeared and began to resorb the bone. No necrosis or degeneration was seen. It is concluded that, under these conditions, F does not exert any toxic action.