Levodopa administered alone or in combination with a peripheral decarboxylase inhibitor is at present the best means available for the control of Parkinson symptoms. It has proved particularly effective in Parkinson's disease and postencephalitic parkinsonism. In these disorders its continued administration for periods that now exceed five years has resulted in sustained therapeutic responses and a significant decrease in mortality rate. Levodopa has been shown to be a safe pharmacologic agent even after long-term usage. However, its potential for inducing side effects makes it essential that patients be carefully screened before use and monitored throughout the period of administration. Though not fully established and lacking FDA approval at this time, levodopa appears to be useful in reversing the symptoms of hepatic encephalopathy and as a diagnostic aid in assessing pituitary disorders as well as uncovering presymptomatic Huntington's chorea.