The surface proteins of dividing and non-dividing subpopulations of rat and mouse thymocytes have been labelled by using a new method of radioiodination. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and autoradiography of the labelled proteins shows distinct differences in labelling between the mouse and rat cells and also, in the case of the rat, between the dividing and non-dividing populations.
