IL-2-dependent cell lines were established from normal peripheral blood T lymphocytes that express neither CD4 nor CD8 differentiation antigens. CD3+,4-,8- cell lines from 15 different donors failed to react with WT31, an mAb directed against the T cell antigen receptor alpha/beta heterodimer. Anti-Leu-4 mAb was used to isolate the CD3/T cell antigen receptor complex from 125I-labeled CD3+,4-,8- (WT31-) T cells. Using detergent conditions that preserved the CD3/T cell antigen receptor complex, an approximately 90 kD disulfide-linked heterodimer, composed of approximately 45- and approximately 40- (or approximately 37-) kD subunits, was coimmunoprecipitated with the invariant 20-29-kD CD3 complex. Analysis of these components by nonequilibrium pH gradient electrophoresis indicated that the approximately 40-kD and approximately 37-kD subunits were similar, and quite distinct from the more basic approximately 45-kD subunit. None of these three subunits reacted with an antibody directed against a beta chain framework epitope. Heteroantiserum against a T cell receptor gamma chain peptide specifically reacted with both the approximately 37- and approximately 40-kD CD3-associated proteins, but not with the approximately 45-kD subunit. CD3+,4-,8- cells failed to transcribe substantial amounts of functional 1.3-kb beta or 1.6-kb alpha mRNA, but produced abundant 1.6-kb gamma mRNA. Southern blot analysis revealed that these CD3+,4-,8- cell lines rearranged both gamma and beta genes, and indicated that the populations were polyclonal. The expression of a CD3-associated disulfide-linked heterodimer on CD3+,4-,8- T cell lines established from normal, adult peripheral blood contrasts with prior reports describing a CD3-associated non-disulfide-linked heterodimer on CD3+/WT31- cell lines established from thymus and peripheral blood obtained from patients with immunodeficiency diseases. We propose that this discrepancy may be explained by preferential usage of the two C gamma genes in T lymphocytes.