Resorption of devitalized bone particles by monocytes grown in culture was stimulated by platelet-derived growth factor (PDGF) in a dose-dependent manner. Bone resorption in response to PDGF was time-dependent with a significant increase over control cultures evident by 72 hours. These data are the first to demonstrate stimulation of bone resorption by PDGF in a specific cell type known to resorb bone in vivo and in vitro.