For patients with hairy cell leukemia, with regard to the cost of interferon treatment, splenectomy is the treatment of choice. In patients who do not respond to splenectomy or have relapses, the drug of choice is interferon alpha, 3 x 10(6) i.u.s.c. daily till remission occurs and then three times per week for a period of 18-24 months. After this period treatment can be terminated, it is however better to proceed permanently with lower maintenance doses. During a relapse interferon alpha is again administered, and if the disease does not respond, it is recommended to test a different interferon preparation or deoxycoformycin or chlorodeoxyadenosine.