Transfer of exponentially growing colonies of Schizophyllum commune to nitrogen-deficient media for 6-60 h resulted in increased general proteolytic activity and decreased extractable protein when compared with controls. A concomitant increase in free radiolabeled leucine was detected in nitrogen-deprived colonies. Radiolabel was found in new surface hyphae following transfer of previously labeled colonies to media containing no label. The concentration of label present in the new growth indicates that this label is likely to have originated from proteolytic release of label from proteins in the older, central portions of the colony. The release of substantial amounts of label into the growth medium suggests that an extra-mycelial pathway may account, at least in part, for translocation of amino acids released by proteolysis.