An IgG1 monoclonal antibody, termed ACM-1, has been shown to react with rabbit T cells, but not Ig+ cells or macrophages. This antibody appears to recognize the same epitope as the previously described 9AE10 antibody and, together with 9AE10, has been used to obtain highly pure and fully functional T- and B-cell populations. However, the relevant epitope does not appear to be homologous to rodent Thy-1 since quantitative absorptions failed to show reactivity with rabbit brain. Furthermore, attempts to obtain in vivo T-cell depletion resulted in larger decreases in white blood cells than would be expected for simple T-cell removal. In vitro assays on enriched neutrophil preparations revealed that 80-95% of these cells were reactive with ACM-1 and 9AE10. Thus, it appears that in the rabbit, T cells and neutrophils share a major epitope.