Biloptin (Schering) and some similar substances, new cholangiocholecystographic contrast media, have been compared with Biligrafin forte (Schering) in a clinical trial on 205 patients. (i) The qualitative criteria used were: visualisation of the biliary ducts as a whole and of the hepatic and lower common ducts before and after ingestion of a fatty meal; demonstration of contrast bile within the duodenum before ingestion of a fatty meal, and visualisation of the gall-bladder. (ii) In addition, a quantitative assessment was made of the length of the longest continuous bile-duct shadow, excluding the cystic duct, before and after ingestion of a fatty meal. Furthermore of the contrast depth, determined densitometrically, of the shadows of the best demonstrated bile duct segment and the gall-bladder before ingestion of a fatty meal, and of the lower common duct after ingestion of a fatty meaL fill) The results showed that Biligrafin is definitely superior to the oral contrast media as a cholangiographic agent whereas the visualisation of the gall-bladder and the lower common duct after ingestion of a fatty meal was not significantly different after both contrast media. (iv) The advantages of the qualitative method are its simplicity and its reflecting the full complexity of the radiographic image instead of merely some measurable properties of its essential structures. Its shortcomings are lack of clarity in the definition of its descriptive categories, the difficulty of maintaining a sufficiently constant standard over a larger series of observations, and the danger of voluntary or involuntary bias. (v) The quantitative method offers a rigid standard for comparison. Its drawbacks, mainly concerning the determination of bile-duct length values, are discussed in detail, It appears noteworthy that the qualitative findings are substantiated and corroborated by the quantitative results and that all essential qualitative findings could be expressed in quantitative terms. Despite its limitations, the quantitative method appears to yield more reliable results, including the demonstration of a layering phenomenon of the contrast media predominant in cases where the bile flow is slow and the patients are bedridden or immobile.