Twenty-two patients with Stages Ia to IVa cutaneous T cell lymphoma were entered into a controlled trial of interferon alfa-2a (Roferon-A). Patients initially received either 3 million IU interferon alfa-2a, or their dosage was escalated to 36 million IU intramuscularly daily for a 10-week induction period. At the end of induction, 14/22 (64%) of patients had an objective antitumor response: three patients had a complete response, ten patients had a partial response (greater than or equal to 50% resolution of clinical disease), and one patient had a minor response. Responders included those with Stages Ia to IVa cutaneous T cell lymphoma, and remissions have lasted at least 4 to 27.5 months. Three patients progressed from a partial to complete response with further treatment, for an overall complete response rate of 27%. Acute flu-like side effects were generally minor and transient. Malaise/fatigue, depression, anorexia, and weight loss were common chronic dose-related side effects and the most frequent reasons for dose reduction or discontinuation of drug. Leukopenia was the most common laboratory side effect and was also dose-related. Recombinant human leukocyte interferon alfa-2a is an effective and well-tolerated single-agent therapy for early and advanced cutaneous T cell lymphoma.