Brief exposure of Chinese hamster ovary cell monolayers prelabeled with [32P]phosphate and [3H]leucine to 1 μg/ml of trypsin under conditions in which cells remain fully viable causes the release of macromolecular 32P and 3H. Whereas ribonuclease treatment was found to affect markedly both the 32P and 3H radioactivity, Pronase treatment had little effect on the macromolecular 32P. Treatment of cells prelabeled with [3H]glucosamine and [32P]phosphate with insolubilized papain also revealed a parallel release of macromolecular glucosamine together with ribonuclease-susceptible macromolecular phosphate. Lactoperoxidase-mediated radioiodination of surface components in cells prelabeled with [32P]phosphate revealed electrophoretic comigration between the 125I and the 32P that are removed from the cells by mild proteolysis. Growth of the cells in Bt2cAMP-testosterone altered the kinetics of release and nature of the macromolecular 32P liberated by proteolysis.