Twenty-three patients with the chronic progressive or intermittent relapsing form of multiple sclerosis (MS) were treated with d-penicillamine over a period from 6 weeks to 12 months. Clinical effect was evaluated using Kurtzke's disability status scale with follow-up lasting from 7 weeks to 15 months. Fifteen patients remained unchanged, 7 became worse and 1 improved after the treatment. Administration of penicillamine to patients with MS resulted in an insignificant lowering of serum IgA, IgG and IgM levels. It is concluded that penicillamine neither prevented the occurrence of relapses nor slowed down the chronic progressive course of multiple sclerosis.