A recent neuropathological study has reported decreased levels of dynorphin A immunoreactivity in striato-pallidal fibers in the brain of a patient with severe Gilles de la Tourette's syndrome (TS). This observation, taken with the neuroanatomic distribution of dynorphin and its broad range of motor and behavioral effects, has led to speculation concerning its role in the pathobiology of TS. We report on the presence of elevated concentrations of dynorphin A [1-8] in the CSF of 7 TS patients, aged 20 to 45 years. The increase in CSF dynorphin was found to be associated with the severity of the obsessive compulsive symptoms but not with tic severity in these patients. Although CSF studies lack the precision necessary to address questions of selective involvement of neuronal system in specific CNS locations, these findings suggest that endogenous opioids are involved in the pathobiology of TS and related disorders. Tourette's syndrome (TS) is a chronic neuropsychiatric disorder of childhood onset that is characterized by multiple motor and phonic tics that wax and wane in severity and an array of behavioral problems including some forms of obsessive compulsive disorder (OCD) (1). Once thought to be a rare condition, the prevalence of TS is now estimated to be one case per 1,000 boys and one case per 10,000 girls, and milder variants of the syndrome are likely to occur in a sizeable percentage of the population (2). Although the etiology of TS remains unknown, the vertical transmission of TS within families follows a pattern consistent with an autosomal dominant form of inheritance (3,4). Neurobiologic and pharmacological data have implicated central monoaminergic and neuropeptidergic systems in the pathophysiology of TS, and basal ganglia structures remain the prime candidates as the neuroanatomical origin for TS and related conditions (1). Endogenous opioids, including dynorphin and met-enkephalin are concentrated in structures of the basal ganglia (5), are known to interact with central dopaminergic neurons (6, 7), and may play an important role in the control of motor functions (8). Post-mortem brain studies have directly implicated opioids in the pathophysiology of Parkinson's disease (9), Huntington's disease (10), and most recently in TS (11). The neuropathological study of Haber et al. (11) reported decreased levels of dynorphin A [1-17] immunoreactivity in striatal fibers projecting to the globus pallidus in the brain of a patient with severe TS. This ovservation, taken with the neuroanatomic distribution of dynorphin and its broad range of motor and behavioral effects, has led to speculation concerning its role in the pathobiology of TS.(ABSTRACT TRUNCATED AT 400 WORDS)