Twenty patients with Parkinson's disease and marked intellectual impairment or dementia participated in a double-blind placebo controlled trial of the nootropic, piracetam. A standardized neurological examination, a neuropsychological test battery, and a functional scale, The Sickness Impact Profile, were completed for all patients. They were then assigned by blind randomization to drug or placebo conditions receiving 3.2 g of piracetam or an identical amount of placebo for 12 weeks. The dose was increased to 4.8 g for an additional 12 weeks. Neurological, psychological, and functional measures were rated as improved, unchanged, or worsened in comparison to baseline performance. Twenty-five percent of the patients did not complete the trial for reasons unrelated to the medication. Although there was a significant improvement on one subtest of the functional scale, no significant effects were demonstrated in cognitive or neurological measures.