Abstract: Bisphosphonate derivatives of hydroxy steroids which are bone resorption inhibitors or bone formation stimulators, the derivatives having at least one group A in place of a hydroxy group on the steroid molelcule, where A is a group of forumla (A) where X is: (i) St--O--CO-- where St is the residue of the hydroxy steroid given by removal of an OH group; or (ii) R.sup.1 --O--CO-- where R.sup.1 is an alkyl, alkenyl, cycloalkyl, aralkyl or aryl group, any of which may optionally be substituted, and the salts and solvates of these compounds. The steroid is typically 17.beta.-oestradiol, oestrone, testosterone, norethindrone, androsterone, norethandrolone or nandrolone. The derivatives can be used in the treatment of bone disorders such as osteoporosis.