One hundred and twenty four patients with follicular lymphoma (32 with Stage III and 92 with Stage IV disease) have been randomized to receive chlorambucil alone or chlorambucil plus interferon alfa-2b. Responding patients are then randomized to receive either interferon alfa-2b maintenance therapy for up to 12 months or no further treatment. One hundred and eight patients are evaluable for response, the remainder are still receiving initial therapy. Clinical remission (complete or good partial remission) was achieved in 42/59 (71%) patients receiving chlorambucil alone and in 27/49 (55%) patients receiving the combination (P = NS). Preliminary analysis of remission duration shows a trend in favour of those patients receiving interferon throughout (P = 0.02). There is no significant difference between the groups in terms of survival, at a median follow up of 2.5 years. Interferon-associated toxicity was minor in most patients but led to discontinuation of therapy in six cases. Larger trials with longer follow-up periods are needed to confirm the beneficial role of interferon in the treatment of follicular lymphoma.