We have employed two-color staining with monoclonal anti-T-cell markers and a broadly reactive, nonbinding site monoclonal anti-idiotype to permit direct visualization of idiotype-bearing T cells in mouse lymph nodes following immunization with phosphorylcholine. Double positive cells peak in incidence on Days 8 to 12, as 17% of total idiotype+ cells but as only 0.7% of T cells. Such cells are antigen-specific, appearing in peripheral lymph nodes only following phosphorylcholine challenge. While Lyt-2+ and L3T4+ subsets are represented and both subsets reexpress the idiotypic determinant following its enzymatic removal, the L3T4+ subset represents the majority of idiotype+Thy-1+ cells. These findings raise the possibility that antigen-specific receptors on T and B cells, encoded by entirely different genetic information, may exhibit similarities in tertiary structure in portions of the molecules not directly involved in antigen binding. This is the first determination of the phenotype and chronology of appearance of idiotype-bearing normal T cells following immunization. It is consistent with previous reports of functionally defined idiotype-bearing T cells and provides direct support for the existence of such cells.