Two patients with subacute sclerosing panencephalitis (SSPE) were treated intramuscularly with recombinant DNA interferon-a2 for 3 and 6 months, respectively. Side effects were minimal. No objective clinical response could be noted. In a patient with stable SSPE, a significant decrease in serum antimeasles antibody levels was observed. This decrease was less pronounced in another patient with evolutive SSPE. The results of this study were compared to findings published previously. The reasons for the lack of clinical efficacy of interferon in SSPE are discussed.