Summary:Four parkinsonian patients received continuous duodenal infusions of levodopa (LD) for severe “on-off” phenomena associated with Sinemet (carbidopa/levodopa) therapy. All patients had marked decreases in motor fluctuations on the infusions compared with tablets. Two factors that appear related to this improvement are the ability of duodenal infusions to produce steadier plasma LD concentrations and/or to maintain LD concentrations above a minimum threshold needed to achieve the “on” state.