A double blind technique was used in testing 3 cholecystographic agents in 726 patients. Graded scoring of radiographs, percentage of diagnostic first day studies, and incidence of adverse effects were evaluated. In the fat free group, a 4.5 g dose of iocetamic acid (Cholebrine) produced the most dense shadows and highest diagnostic yield and iopanoic acid (Telepaque) the least dense and lowest diagnostic yield. The difference in density and diagnostic yield between tyropanoate sodium 3.0 g (Bilopaque) and iocetamic acid 4.5 g was not statistically significant. A fatty meal significantly increased density and diagnostic yield of iopanoic acid and appeared to improve its absorption.