The stratification (layering) phenomenon in the gallbladder is a source of errors in interpretation of intravenous cholangiography. It may mimic stones that do not exist or conceal stones that do. To avoid false-positive or false-negative interpretations, it is suggested that delayed films be taken at 4 hours in cases which demonstrate a layering phenomenon. By this time, a normal gallbladder will be homogeneously opacified and a diseased one will reveal its stones. Horizontal beam roentgenograms are mandatory for complete evaluation.