We examined the distribution of 99mTc-MDP in 12 late-stage nontraumatic necrotic femoral heads by autoradiography and compared this to the histology of adjacent sections. A widespread fibrocartilaginous metaplasia, and enchondral ossification was observed in the demarcation zone. The highest uptake of the isotope was seen at the provisional calcification in areas with enchondral ossification in the demarcation zone. We concluded that the uneven distribution of 99mTc-MDP was mainly due to the remodeling processes.