Three patients at Stage II of subacute sclerosing panencephalitis (SSPE) were treated with semipurified alpha-interferon (IFN) using different combinations of intrathecal and intravenous routes: 1 x 10(6) IU of alpha-IFN were given every other day up to a total of 15 x 10(6) IU. Transient improvement of neurological symptoms and electroencephalogram were noted in all 3, while cognitive function slightly improved in 2 of them. Clinical benefits gradually disappeared 2 to 6 months after cessation of IFN. Intrathecal antibody production did not change substantially, but CSF Leu 3a/Leu 2a ratio appeared to increase. No significant side effects were observed, except for a mild meningeal inflammatory reaction after each intrathecal administration of IFN.