WASp-null osteoclasts are defective in bone resorption in vivo. Weight-matched 22-week-old WASp-null and SV129 wild-type mice were ovariectomized (ovx) or sham ovariectomized (sham). Animals were culled 15 days after ovariectomy, then femurs were removed from each animal, freed of soft tissue, and fixed in 10% formalin in PBS and embedded in paraffin wax. Sections were stained with either toluidine blue for assessment of bone volume (A), eroded surface (B), or TRAP to quantify the percentage of bone area occupied by osteoclast surface (C) and osteoclast number per millimeter (D). The graphs represent the mean ± SEM values. ^*P < .05 (Student t test) compared to sham-ox.