L-Dihydroxyphenylalanine (l-dopa), effective in the treatment of Parkinson's disease, frequently causes postural hypotension and arrhythmias. The large doses used may alter peripheral adrenergic function. To evolve a rational anesthetic management for the increasing number of parkinsonism patients maintained on l-dopa therapy, central and peripheral catecholamine stores and the turnover of myocardial norepinephrine (NE) as affected by L-dopa were studied in rats. Large doses of l-dopa (100–200 mg/kg, i.p.) increased die concentration of dopamine (DM) in the brain without changing the concentration of NE significantly. DM accumulated in the heart following l-dopa treatment, accompanied by a decrease in XE concentration. After labelling of the myocardial NE store with tracer doses of5H-NE, treatment with l-dopa caused a more rapid decline of specific activity of myocardial NE. Therefore, DM may displace NE from peripheral sympathetic nerve endings and interfere with adrenergic transmission.