Disclosed are x-ray contrast compositions for oral or retrograde examination of the gastrointestinal tract comprising a polymeric material capable of forming a coating on the gastrointestinal tract and an x-ray producing agent of the formula ##STR1## and methods for their use in diagnostic radiology of the gastrointestinal tract wherein ##STR2## Z=H, halo, C.sub.1 -C.sub.20 alkyl, cycloalkyl, lower alkoxy, cyano, where the alkyl and cycloalkyl groups can be substituted with halogen or halo-lower-alkyl groups;R=C.sub.1 -C.sub.25 alkyl, cycloalkyl, aryl or halo-lower-alkyl, optionally substituted with halo, fluoro-lower-alkyl, lower-alkoxy, hydroxy, carboxy or lower-alkoxy carbonyl, lower-alkenyl, lower-alkynyl, lower-alkylene or lower-alkoxy-carbonyloxy,n is 1-5;y is 0-4; andw is 1-4.