SummaryTwo cloned murine cell lines. FD.C/1 and 32Dcl‐23 exhibit switching of lymphokine‐dependent growth states. The bone marrow‐derived FD.C/1 and 32Dcl‐23 cell lines are normally grown in culture medium supplemented with inierleukin 3 (IL3). The replacement of IL3 with interleukin 2 (IL2) in the medium results in an increase in IL2 receptor expression in FD.C/1 and 32Dcl‐23 cells and the switching of cells lo an IL2‐dependent growth state. We have compared patterns of protein and phosphoprotein synthesis, as well as the expression of the c‐abl, c‐ras, c‐myb, and c‐fos oncogenes in these cell lines maintained in IL3‐ and I L2‐dependent growth states. The synthesis of a series of proteins and phosphoproteins are identified with each of the lymphokine‐dependent growth states. All of the oncogenes examined are expressed in both IL2‐ and lL3‐dependent cells and are not altered by phenotypic changes in lymphokine growth dependence. The relationship of oncogene expression to intracellular pathways regulated by lymphokine‐receptor interactions is considered.