Since the introduction of adenosine deaminase analogues the vast majority of patients with Hairy cell leukemia obtain lasting complete remission. In this report we describe our experience with 2 CdA in 18 patients with Hairy cell leukemia (HCL). Ten of these had failed previous interferon therapy, 6 were splenectomized before and of these, 4 had also received interferon. Sixteen of the 18 patients receiving 2 CdA achieved complete remission (CR), 1 patient is in good partial response (GPR) and 1 patient has relapsed. These results are in keeping with those reported from other larger centers and confirm the efficacy of 2-CdA. In this report IL-2 receptor (sIL-2R) levels were performed in most of the patients and found to be an accurate indicator of disease activity. Mean levels prior to therapy were 17200 U/ml (+/- 2500) and after successful therapy 970 U/ml (+/- 160). We confirm that 2-CdA treatment is the treatment of choice in HCL and suggest that sIL-2 levels be used as a parameter of disease activity.