Bisphosphonic acids and esters

A compound of formula I ##STR5## in which R.sub.1 is a straight or branched, saturated or unsaturated aliphatic or alicyclic C.sub.1 -C.sub.10 hydrocarbon radical, an aryl or an aryl-C.sub.1 -C.sub.4 -alkyl radical, R.sub.1 if desired being unsubstituted or substituted with straight or branched C.sub.1 -C.sub.4 -alkyl, amino, C.sub.1 -C.sub.4 -alkylamino, di-(C.sub.1 -C.sub.4 -alkyl)-amino, carboxy, C.sub.1 -C.sub.4 -alkoxycarbonyl, hydroxy, C.sub.1 -C.sub.4 -alkoxy, phenoxy, mercapto, C.sub.1 -C.sub.4 -alkylthio, phenylthio, halogen, trifluoromethyl;

• R.sub.2 stands for hydrogen, C.sub.1 -C.sub.8 -alkyl, aryl-C.sub.1 -C.sub.4 -alkyl or halogen;
• X is O or S, and n is an integer from 0 to 2;
• with the provisos that R.sub.2 cannot be hydrogen or methyl if n=O and R.sub.1 is methyl and that R.sub.2 cannot be hydrogen or methyl if n=O and R.sub.1 is unsubstituted n-butyl, n-pentyl or n-hexyl;
• and pharmaceutically acceptable, non-toxic salts and in the body easily hydrolyzable esters thereof.