In four selected, commercial barium sulfate preparations, viscosity, surface tension and particle size were measured; examined were agglomeration, sedimentation and homogeneity in vitro. For the clinical-radiological examination, an evaluation scheme has been developed containing the following criteria: uniformity and thickness of contrast medium layer, demonstration of the areae gastricae, clearness of gastric contour, and vesiculation. A blind study, encompassing about 100 double contrast examinations of each preparation, ascertained the usability of this scheme. Significant differences could be detected among the four contrast media. The barium sulfate suspension which was rated the highest lay within a viscosity range of 50-90 cP, had a particle diameter of 0.2-1.6 micrometer and showed the least degree of agglomeration. Results of the in vitro examinations, when compared to the clinical tests, lead to the conclusion that both, gastric mucous and contrast medium additives, may exert considerable influence on the pictorial quality of the above defined criteria.