The present invention produces alkyldiphosphonic acid derivative of the general formula: ##STR1## wherein Het is a heteroaromatic five-membered ring containing to 3 heteroatoms which can be partly hydrogenated and optionally substituted one or more times by alkyl, alkoxy, phenyl, cyclohexyl, cyclohexylmethyl, halogen or amino, and two adjacent alkyl substituents can together also form a ring, Y is a hydrogen atom or a lower alkyl radical, X is a hydrogen atom, a hydroxyl group or an amino group optionally substituted by lower alkyl and R is a hydrogen atom or a lower alkyl radical, with the proviso that Het is not a pyrazole ring; as well as the pharmacologically acceptable salts thereof.The present invention also provides processes for the prepearation of these compounds and pharmaceutical compositions containing them useful for the treatment or prophylaxis of calcium metabolism disturbances or disease as for example osteoporosis, Bechterew's disease, bone metastases, urolithiasis, heterotropic ossifications, rheumatoid arthritis osteoarthritis or degenerative arthrosis.