We treated 26 patients with hairy cell leukaemia (HCL) with 2-chlorodeoxyadenosine, including nine with abdominal lymphadenopathy and of whom two had HCL-variant; 18 were previously treated. The overall response in 23 evaluable HCL patients was 100% with 87% complete remission (CR). The CR rate was 57% in patients with abdominal lymphadenopathy. Neither of the patients with HCL-variant achieved CR. Of four patients who had become refractory to 2'-deoxycoformycin, two achieved CR and one partial remission (PR). The lower response in HCL with abdominal lymphadenopathy supports the view that this represents a more resistant form of the disease.