c-Fms inhibition blocks osteoclast differentiation. Bone marrow cells from naïve BALB/c mice were treated with macrophage colony-stimulating factor (M-CSF) alone for 24 hours and then transferred to plates with either dentine disks (a, b) or osteologic disks (c) and treated with M-CSF and receptor activator of nuclear factor-kappa B ligand (RANKL) ± GW2580 or imatinib. (a) Representative images showing reduction in tartrate-resistant acid phosphatase-positive (TRAP+) cell numbers following treatment with imatinib or GW2580. For quantification, the dentine disk area that stained positive for TRAP+ multinucleated cells (b) and the degree of pit formation in osteologic disks (c) are expressed as a percentage of the area stained or of the pit formation detected following treatment with M-CSF and RANKL. The data shown are representative of at least two independent experiments. Values are the mean ± standard error of the mean. **P < 0.01 compared with cells treated with M-CSF and RANKL alone (b, c).