Mononuclear phagocytes have been implicated as important cellular elements in the process of bone resorption. We have postulated that the recruitment and migration of mononuclear phagocytes to bone occurs via a mechanism(s) in which bone-derived chemotactic factors (BDCF) are released from foci undergoing resorption. In the experiments presented here we have used newborn mouse calvaria and examined a variety of extraction protocols, both dissociative and non-dissociative, as means of obtaining stable and reproducible chemotactic activity for mouse peritoneal macrophages. Chemotaxis and chemokinesis were assessed using a multi-well chamber modification of the Boyden transfilter method. Further, we have attempted to purify the BDCF by both molecular sieve and anion exchange chromatography. Our results indicated that non-dissociative extraction with 0.5 M EDTA in the presence of 1% DMSO yielded the most potent and reproducible chemotactic activity. The results of molecular sieve and anion exchange chromatography suggested that there were several BDCF activities in these preparations and that their molecular weights were probably in the range of from 14,000-67,000 daltons. Anion exchange chromatography also demonstrated the presence of a fraction, eluted with 2 M NaCl, with high chemotactic activity and minimal protein concentration. These observations confirmed the suggestion that there are several macrophage chemotactic factors in bone which have as yet to be identified, and suggest methods for pursuing their isolation.