Transformation by the v-sis containing simian sarcoma virus (SSV) is believed to be mediated by constitutive production of a platelet-derived growth factor (PDGF)-like molecule and its interaction with the PDGF receptor. SSV-transformed nonproducer NRK cells release into their tissue culture supernatant a high-molecular-weight factor (150-300 kDa) with biological activities closely resembling those of human PDGF. The partially purified high-molecular-weight factor competes with 125I-PDGF for receptor binding and leads to growth stimulation and anchorage-independent growth of normal cells. All these activities can be blocked by antibodies against PDGF and SSV-NP cells. The formerly described SSV transformation-specific glycopeptide (Thiel and Hafenrichter, 1984), now termed gp200sis, is recognized by the same specific antibodies and shows a striking resemblance in size. We conclude that gp200sis is responsible for the described PDGF-like activities.