The long-term effect of L-dopa in 3 patients with progressive supranuclear palsy is described and 10 other cases previously reported are summarized. L-dopa has a significant effect on the parkinsonian features of PSP but does not have any significant effect on the specific non-parkinsonian features such as ophthalmoplegia and neck dystonia. The implications of this difference are discussed in relation to the pathophysiology of the separate symptoms.