Earthworm extract does not affect the proliferation of osteoclasts. RAW 264.7 cells were seeded in 48-well plates and allowed to adhere for 1 day. Osteoclast differentiation from RAW 264.7 cells was induced with 50 ng/ml RANKL in α-MEM for 6 days. Osteoclasts were then cultured with PBS as a control or different concentrations of earthworm extract for 2 days. Osteoclast viability was measured by MTT assay.