During examinations of viable leukocytes from many leukemic and nonleukemic patients, peculiar cells called "hairy" cells were seen in the blood from 2 patients. These cells were characterized by numerous short, thin villi projecting from the surface of the cells. In one patient, some of these cells had one or more cytoplasmic masses. The nuclei were oval or crescentic, eccentrically placed, and some had small nucleoli. The cells did not flatten on glass, did not phagocytize latex particles, and were resistant to irradiation with 2000 r. The cells were considered to be identical to the neoplastic lymphoid reticulum cells of Mitus et al.1 Both patients with hairy cells had large spleens, moderate anemia, and thrombocytopenia. Radiotherapy of the spleen of one patient resulted in a prompt leukopenia and a delayed decrease in the size of the spleen. This patient is alive and asymptomatic 21 months after diagnosis. The second patient’s thrombocytopenia was relieved by splenectomy. He is asymptomatic now, 11 months after diagnosis. Hairy cells are still present in small numbers in the blood of both patients. The pathologic hairy cells in the blood were similar to "flagellated" cells seen in suspensions from several hyperplastic lymph nodes. The flagellated cells were relatively few in number, large, with numerous long, thin cytoplasmic projections and round, oval or crescentic nuclei, some of which had small nucleoli. The flagellated cells were resistant to irradiation and probably were identical to the "phagocytic reticular cells" of Sundberg.12

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