Alpha-interferon (IFN) and 2'-deoxycoformycin (dCF) both exhibit substantial activity in the treatment of hairy cell leukemia (HCL). Anecdotal reports have suggested that patients who failed IFN could achieve durable responses with dCF, although the frequency with which this was said to have occurred was unknown. We reviewed the available data on the responsiveness of HCL to dCF after IFN therapy by analyzing cases reported in the literature and those treated under the Special Exception mechanism of the National Cancer Institute, Division of Cancer Treatment. Of 60 such cases identified there were 22 (37%) "compete responses" and 22 (37%) "partial responses" for a total response rate of 74%. Responses appeared to be durable in many cases, lasting up to 2 years at the time of reporting. dCF is an active agent in HCL both as initial therapy and for the salvage of patients who have failed IFN. The relative activity of these two agents and the optimal strategies for their use are currently under investigation in ongoing clinical trials.