Immunocytochemical staining of aggressive NK cell leukemia/lymphoma (case no. 39), using the labeled avidin-biotin alkaline phosphatase system. The smears were prepared from mononuclear cells separated by density gradient centrifugation using Ficoll-Isopaque. (A) The cells are positive for CD2. (B) There is no reactivity for Leu4/CD3; the strongly stained small lymphocytes serve as internal positive controls. (C) The cells are reactive for CD56 (NKH1).