Spectrographic studies and determinations based on periodate oxidations show that the Mn content of ox femur is of the order 0.27-0.51 ppm. depending on the type of bone, compact or cancellous. Irrespective of the type this corresponds to about 1.4 ppm. expressed on the ash. Most of the Mn is associated with the inorganic matrix, but a small proportion is bound to the organic matrix. Little Mn, if any, accompanies the water-soluble alkaline phosphatase.