1. The concentration of lithium in bone was determined after various periods of lithium administration in rats of differing ages and also after discontinuation. Lithium content was determined in human bone of three lithium-treated and two control subjects.
2. There was an inverse relationship between age at commencement of treatment and the final bone lithium content. This suggests that lithium is incorporated into the mineral of rapidly growing bone.
3. The loss of lithium from bone after discontinuation of medication indicates that one fraction is lost rapidly, and a large fraction remains and is lost very slowly.
4. Analysis of human bone from three subjects after lithium discontinuation shows that concentrations exist similar to those of rat bone. Control human bone had a lithium concentration which was similar to that of control rat bone.