Rabbit and monoclonal antibodies to human myeloid leukemia cells, monocytic leukemia cells and human thymocytes have shown the existence of common T-cell/myeloid/monocyte antigens. For this reason, the specificity of a series of monoclonal antibodies to human T-cells (OKT 1, 3, 4, 5, 6, 8, 9, 10; and NA1/34) was tested by immunofluorescence (cytofluorograph) and complement-mediated cytotoxicity against human myeloid leukemia and normal blood cells and leukemic cell lines. In addition, an immunohistological analysis of the specificity of OKT4, 9.3, Leu 3a, OKT3 and NA1/34 antibodies was performed using normal lymphoid tissues and a sensitive immunoperoxidase technique. Normal human peripheral blood mononuclear cells reacted with OKT3 ("pan T-cell", mean 54%), OKT4 ("helper T-cell", mean 35%) and OKT 5/8 ("suppressor T-cell", mean 18%) as previously reported. However, OKT3 reacted with the cell lines K562 (myeloid), RC2a and THP-1 (monocytoid) and U937 (macrophage) as well as with cells from 9/65 myeloid leukemia patients. OKT4 reacted with the cell lines HL60 (promyelocyte), RC2a and U937 and also with cells from 6/60 myeloid leukemia patients. OKT5 reacted with the cell lines K562 and THP-1. OKT1 ("pan T-cell") reacted with THP-1 and with myeloid and monocytic leukemia samples (5/32) as did OKT6 ("cortical thymocyte") (3/32). OKT10 ("common thymocyte") reacted with a range of leukemia cell lines (B-cell, pre- B-cell and macrophage) as well as 7/21 myeloid leukemia samples. In tissue sections Leu 3a, (9.3 and OKT4 to a lesser extent), stained paracortical lymphocytes, plus subcapsular and medullary macrophages, and dendritic cells present within the paracortex.(ABSTRACT TRUNCATED AT 250 WORDS)