The present invention concerns the use of .gamma.-glutamyl-peptide, for example .gamma.-L-glutamyltrans-S-1-propenyl-L-cysteine sulfoxide, in the treatment or prevention of diseases or conditions which are characterized by increased bone resorption, such as Paget's disease, tumor-induced bone disease or osteoporosis, inhibits dose-dependently the resorption activity of osteoclasts, the minimal effective dose being about 2 mM.