Bone marrow aspirates and biopsies from ten normal donors were stained directly with monoclonal antibodies specific for lymphocyte, monocyte, and myeloid antigens, and were analyzed by flow cytometry. To avoid cell loss, lymphocytes were not specifically isolated prior to staining. T cells comprised 46% of aspirate lymphocytes and 22% of biopsy lymphocytes. Further, the Leu-3:Leu-2 ratio of bone marrow T cells was below 1.0. B cells comprised 8% to 11% of bone marrow lymphocytes in both aspirates and biopsies, and there was a substantial percentage of cells in the lymphocyte window that was negative for all B and T cell markers. The lymphocyte window had very little myeloid contamination; however, when the myeloid window was examined, staining was greater than 90%.