Westudied 25 Japanese patients with hairy cell leukemia (HCL) and found a manner in which HCL can be divided into two subtypes. In each patient, hairy cells (HC) showed striking surface hairs and reacted with HC-specific antibodies ( aLeu-M5 and « HC-M). Twenty of the 25 patients had HC characterized by round nuclei with dense nuclear chromatin, weak tartrate-resistant acid phosphatase (TRAP) activity and the phenotype of low density surface immunoglobulin (SIg)+ , Tac~. In this group of 20

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... ents, the male to female ratio was low, and there was frequent leukocytosis. Onthe other hand, the remaining 5 patients showeda high male to female ratio and a normal or decreased leukocyte count. HChad folded nuclei, strong TRAPactivity and the phenotype of high density SIg+ , Tac+. The features of the latter patients are consistent with those of HCLin Western countries, while those of the former group appear to indicate a unique variant ofHCL.