The immunomodulatory action of inosiplex, a drug frequently used in subacute sclerosing panencephalitis (SSPE), varies according to its dose and the subjects’ immune status. In order to assess its effect in children and adolescents with SSPE, inosiplex (25-50 mg/kg/day) was given to 9 patients aged 7-17 years. Their clinical and immunologic status was evaluated before and after 2 months’ treatment. Lymphocyte mitogenic response decreased in 6 cases. These patients were clinically stable or improving during this period. Changes in cytotoxicity (increased in 5/6 patients) and suppressor cell function (increased in 4/8 and decreased in 4/8) were not significant nor associated with any particular clinical course. Our results suggest that inosiplex at this dose is more likely to suppress lymphocyte proliferation in SSPE and this is not due to advancing disease. Longer follow-up of clinical and laboratory findings seems to be indicated in therapeutic trials in SSPE.