The purpose of this study was to use affinity-purified polyclonal antibodies produced against a synthetic peptide corresponding to the joining (J) region of a human T cell receptor beta chain to characterize antigen receptor expression on subpopulations of human lymphocytes. The synthetic peptide used was ANYGYTFGSGTRLTVV, corresponding to the J segment of the human beta-chain gene YT35. Biochemical characterization has previously demonstrated binding of anti-J beta peptide antibodies to the alpha/beta heterodimer and to certain immunoglobulin light chains. Flow cytometric analysis of normal human peripheral blood lymphocytes performed here, using affinity-purified antibodies to the J beta peptide, showed expression of the epitope on 50-60% of CD20 (B1)-positive B lymphocytes, and on 40-50% of CD8-positive T lymphocytes. Only background levels were observed on CD4-positive T cells.