Hairy-cell leukemia is a well-characterized, pathologic disorder. The majority of cases are B lymphocyte in origin with circulating hairy cells, splenomegaly, and, not infrequently, pancytopenia included in the clinical findings. Observation, splenectomy, glucocorticoids (ie, for vasculitic manifestations), and alkylating agents are the currently recommended treatment for this disease. Recombinant interferon alpha may become the treatment of choice for individuals with progressive disease after splenectomy. An understanding of the mechanism of action of recombinant interferon alpha may shed light on the pathways of interferons in general, as well as provide insights into the pathogenesis of this particular proliferative disorder.