Fifteen previously untreated patients with B-chronic lymphocytic leukemia (CLL) (12 in Binet's stage A, 2 in B and one in C) were treated with recombinant alpha-IFN (2a or 2b). Subcutaneous dosage regimens (3 MU three times a week or 1.5 MU/daily), given for at least 14 weeks, lowered the lymphocyte count giving an initial reduction of 17-75%. When therapy was interrupted in 11 patients, the decreased lymphocyte numbers tended to increase again. The mean lymphocyte doubling time was of 16.3 months. No case of disease progression during alpha-IFN therapy could be observed. These results demonstrate that alpha-IFN may be effective in the early phase of B-CLL. It is too early to draw conclusions on the possible long term benefits.