Binding of cognate Radiation leukemia virus (RadLV) by the C6VL/1 thymoma involves a subset of TCR molecules in association with CD4 molecules expressed by that cell line. A CD4- variant of C6VL/1 has now been isolated which also has RadLV binding capacity. Stable expression of the TCR, class I, and CD5 molecules but not Thy1.2 and CD4 molecules has been demonstrated, and the C6VL/1 origin of this cell has been confirmed by Southern blot analysis using probes specific for the TCR beta chain gene. This cell line has maintained binding capacity for RadLV/C6VL prepared as an immunoabsorbent matrix, but unlike the parent C6VL/1 cell line, binds significantly less well to the related RadLV/VL3 isolate. Binding of the variant cell line to RadLV/C6VL can be completely inhibited by anti-clonotypic antibody to the TCR but only weakly by anti-H-2Kb antibody used at the same concentration. These data suggest that the TCR on C6VL/1 can interact with RadLV in the absence of any co-receptor function of CD4 and implicates the TCR as a sufficient receptor for retrovirus.