The sensitivities of five X-ray films commonly used for autoradiography of whole-body sections and thin-layer chromatograms were determined. The films tested were Kodak NS-2T, XAR-5, Industrex C, Agfa-Gevaert Osray M3 and CEAverken Singul-X. The order of sensitivity, from greatest to least, was found to be NS-2T, Osray M3, XAR-5, Singul-X and Industrex C. Increases in sensitivity following extended development were demonstrated for Industrex C. A literature review has revealed confusion in the use, in whole-body autoradiography, or various measures of autoradiographic response, which, in view of the simple relationship between radiographic optical density and absorbed dose, need not have arisen.