Iodinated esters

A compound which is a water-insoluble iodinated ester of the formula (I):

• ##STR3## in which R.sup.1 is a substituted or unsubstituted C.sub.1-20 aliphatic, C.sub.7-20 -araliphatic or C.sub.6-20 aryl group or a 5 or 6 membered heterocyclic group having one or more hetero atoms selected from O, S and N;
• R.sup.2 is hydrogen or a substituted or unsubstituted C.sub.1-6 aliphatic, C.sub.6-10 aryl or C.sub.7-20 araliphatic group;
• and
• R.sup.3 is a group as defined above for R.sup.1, which may be the same as or different from R.sup.1,
• or R.sup.2 and R.sup.3 together represent a substituted or unsubstituted C.sub.1-4 alkylene group,
• the compound containing at least one iodine atom and being metabolisable to products which are soluble in body fluids and are physiologically acceptable.