Previously, we reported the monoclonal antibody detection of transformation-associated proteins (TAP) in ts110 murine sarcoma virus-transformed normal rat kidney (6M2) cells (Chan et al., 1986). In this study, we used the same monoclonal antibody to investigate the subcellular localization, the fate and the mitogenic activity of TAP, as well as the correlationship between TAP synthesis and the expression of transformation properties of 6M2 cells. It was found that TAP were localized in the cytoplasm (probably the Golgi apparatus) of 6M2 cells. TAP were found as three intracellular polypeptides (mol wt of 66K, 63K, and 60K, respectively), and were rapidly released into extracellular medium. Upon release, TAP changed to two extracellular polypeptides (mol wt of 68K and 64K, respectively). Furthermore, the synthesis of TAP was temperature sensitive and correlated closely with the expression of transformation properties of the 6M2 cells. TAP have been purified by monoclonal antibody-affinity column chromatography and found to have a synergistic effect with insulin in stimulating the DNA synthesis of normal rat kidney cells.