Most of the monoclonal antibodies (MoAbs) to T-lymphocyte subsets are, with few exceptions thought to recognize antigens (Ags) unique to T-cells. The authors examined the distribution of cells reacting with MoAbs to the helper/inducer (OKT4, anti-Leu-3a,b) and suppressor/cytotoxic (OKT8, anti-Leu-2a) T-lymphocyte subsets and to "pan T" Ags (anti-Leu-1, anti-Leu-4) in sections from frozen human spleen. In addition to recognizing lymphocytes in the T-zone (periarteriolar lymphoid sheaths), MoAbs to the helper/inducer and suppressor/cytotoxic T-cell subsets reacted distinctly with the red pulp sinusoidal lining cells. MoAbs to "pan T" Ags also reacted with T-zone lymphocytes but did not react with sinusoidal lining cells. MoAbs to the helper/inducer and suppressor/cytotoxic subsets of T-lymphocytes do not appear to identify Ags unique to these cells.