Thirty-seven eligible patients with advanced non-Hodgkin's lymphoma of low-grade, T-cell intermediate- and high-grade histology were treated with pentostatin (2'-deoxycoformycin, dCF) 4mg/m2 i.v. weekly for 3 weeks and then every 14 days to be followed after 3 doses by the same dosage every 4 weeks until maximum response or progression. Only patients with no more than two chemotherapy regimens were entered in this trial. All patients had measurable disease, performance status of 1,0 and 2 and adequate bone marrow, renal and liver function. Five of 37 eligible patients experienced a partial response of 8 months' median duration (range 7-12). The response rate was 17% in low-grade, 8% in T-cell intermediate- and high-grade and 14% in cutaneous T cell lymphoma. The only eligible patient with Hodgkin's disease underwent progression while on treatment. One case presented with grade 3 leukopenia and another one died of septicaemia, possibly treatment-related. Elevated but reversible creatinine levels were observed in 13% of patients and conjunctivitis in 7%. The toxicity of dCF at this low-dose schedule was acceptable, but the therapeutic activity in pretreated patients with low-grade, T-cell intermediate- and high-grade and cutaneous T-cell lymphomas was limited.