Abstract: The invention provides low viscosity iodinated aryl compounds, useful as X-ray contrast agents, of formula C6R6 wherein three non-adjacent R groups are iodine and the remaining R groups are non-ionic, hydrophilic moieties, said compound being water soluble at 20° C. to a concentration of at least 350 mgl/ml and which in aqueous solution at 20° C. at a concentration of 350 mgl/ml has a viscosity no greater than 13.8 mPas.

Abstract: The invention provides low viscosity iodinated aryl compounds, useful as X-ray contrast agents, of formula I ##STR1## (wherein n is 0 or 1, and where n is 1 each C.sub.6 R.sub.5 moeity may be the same or different; each group R is a hydrogen atom, an iodine atom or a hydrophilic moiety M or M.sub.1, two or three non-adjacent R groups in each C.sub.6 R.sub.5 moiety being iodine and at least one, and preferably two or three, R groups in each C.sub.6 R.sub.5 moiety being M or M.sub.1 moieties; X denotes a bond or a group providing a 1 to 7 atom chain linking two C.sub.6 R.sub.5 moieties or, where n is 0, X denotes a group R; each M independently is a non-ionic hydrophilic moiety; and each M.sub.1 independently represents a C.sub.1-4 alkyl group substituted by at least one hydroxyl group and optionally linked to the phenyl ring via a carbonyl, sulphone or sulphoxide group, at least one R group being an M.sub.1 moiety; with the proviso that where n is zero either at least one M.sub.