Ten previously untreated patients with early B cell chronic lymphocytic leukemia (B-CLL) (seven in Rai's stage 0, three in stage I) were given recombinant alpha 2-interferon (alpha 2IF) (2 X 10(6) U/m2 intramuscularly three times a week for a minimum of 14 weeks) to assess its effectiveness. All patients were evaluable for response to therapy and toxicity. No complete response was achieved. In all cases a definite, although transient reduction in the absolute number of peripheral blood lymphocytes was observed. In eight patients an increase in the absolute number of granulocytes was detected. None of the patients experienced severe hematologic toxicity. Fatigue, malaise, and fever were the more common side effects, but all patients were able to finish their treatment as planned. The results of this pilot study suggest that low doses of recombinant alpha 2-IF have some activity in early and previously untreated B-CLL and that further studies of IF effectiveness in B-CLL seem warranted.