Tourette's syndrome (TS) is a complex inherited neuropsychiatric disorder that is characterized by multiple motor and phonic tics. Stress-related fluctuations in symptom severity and medication responsiveness are common, and patients often report that tics are worsened by fatigue, emotional trauma, and anxiety. We examined the effects of lumbar puncture (LP) stress on plasma adrenocorticotropin (ACTH) and cortisol, urinary catecholamines, and self- and clinician ratings of anxiety in 13 medication-free TS patients and 10 normal controls, ages 17 to 41 years. The TS patients secreted significantly more ACTH than the normal controls in response to the stress of the lumbar puncture. Compared to the controls the TS patients had significantly greater postLP mean and postLP peak ACTH levels. The TS patients also excreted significantly more norepinephrine in the 20 hr preceding the lumbar puncture and reported higher levels of anxiety before and during the procedure than the controls. In addition, urinary norepinephrine excretion of the TS patients was significantly correlated with clinician ratings of tic severity. The results were not related to current levels of depression and anxiety. Taken together, these findings suggest that a subset of TS patients may be characterized by heightened reactivity of the hypothalamic-pituitary-adrenal axis and related noradrenergic sympathetic systems.