The detection of radiolabeled proteins is of fundamental importance in experimental biology. 35 S- and 14 C-labeled proteins can provide investigators with information about protein expression, synthesis, and degradation. Moreover, posttranslational modifications, such as phosphorylation, can be studied with the use of 32 P. Traditional methods for detecting radiolabeled proteins involve somewhat lengthy exposures to photographic film. Quantitation from film-based autoradiography can be achieved by densitometry of repeated and various exposures to films because of the small linear dynamic range of photographic film.