Bone remodelling is process of constant resorption and formation of a bone. Osteoclasts are the cells responsible for bone resorption. Deregulation of osteoclast differentiation, activity or function can cause severe diseases, such as osteoporosis, osteopetrosis or rheumatoid arthritis. Advances in molecular biology of osteoclasts and osteoimmunology open new approaches for the specific and efficient therapy.

        Key words: osteoclasts, differentiation, activity, osteoporosis, therapy.