The osteoclast is a large multinucleate cell formed from the fusion of mono-nuclear precursor cells of hemopoietic origin Unique markers of the osteoclast have been difficult to identify. Widely used techniques, such as histochemical location of tartrate-resistant acid phosphatase, and response to calciotropic hormones do not distinguish effectively between osteoclasts and non-osteo-clastic cells The only unequivocal evidence of osteoclast activity is the ability of the cells to excavate authentic resorption lacunae in vivo and in vitro (1.