Previous studies utilizing NP (4-hydroxy, 3-nitrophenyl acetyl hapten)-specific, T suppressor hybridomas have indicated that expression of TCR-alpha, but not TCR-beta, mRNA is required for expression of Ag-specific suppressor factor bioactivity. Suppressor-effector factor has been shown to be Ag specific and I-J restricted. Although the expression of TCR-alpha mRNA was necessary for suppressor activity, the role of TCR-alpha, as it pertained to the functional properties of T cell suppressor factor (TsF), was not established. To determine which properties of TsF could be accounted for by TCR-alpha expression, TCR-alpha cDNA, derived from NP-specific, suppressor T cell (Ts) hybridomas, was transfected into recipient Ts hybridomas of a second Ag specificity. The resulting heterologous transfectants displayed NP-specific, genetically restricted TsF activity. The Ag specificity corresponded to that of the TCR-alpha donor; however, the genetic restriction was influenced by the recipient cell, implying that TCR-alpha did not control genetic restriction of the TsF. Examination of TCR-beta expression in one of the MHC-restricted transfectants indicated that the genetic restriction of TsF could not be accounted for by TCR-beta gene products. The data support the conclusion that TCR-alpha expression is not only obligate for TsF bioactivity, but that the Ag specificity of the TCR-alpha dictates the Ag specificity of the resulting suppressor factor.