Levamisole seems to regulate cell-mediated immunity by restoring T-cell function. Since a deficiency of T lymphocytes has been described by various authors in multiple sclerosis patients. Of the 85 patients involved in the trial, evaluation of functional and neurological scores was possible in 54 (32 with placebo and 22 with levamisole). The mean follow-up period was 2 years. This double-blind controlled study indicates that both neurological function and disability significantly deteriorated in the placebo-treated patients, but remained fairly stable in the levamisole-treated group. Since the difference between both groups was not significant, no levamisole effect was demonstrated on progression in multiple sclerosis. With the exception of one case of granulocytopenia (which had no clinical effect), no drug-related changes could be demonstrated. This contrasts with the general impression that this immunomodulator agent might be harmful to patients with multiple sclerosis. The fact that during this blind study both annual relapse rate and disability score remained more stable in treated patients with severe disability suggests that, while waiting for a more effective treatment, long-term levamisole therapy could be useful in patients with multiple sclerosis.