A dopaminergic agonist, bromocriptine, has been studied in patients with idiopathic parkinsonism complicated by severe “on-off” phenomena induced by levodopa. In a “blind” self-evaluating within-patient comparison, fluctuations in clinical state still occurred when levodopa (with or without carbidopa) was replaced with bromocriptine, but they were significantly reduced in frequency. The observation that on-off phenomena can be induced by bromocriptine complicates interpretation of these episodes in terms of pharmacokinetics of levodopa. There may be variations in receptor sensitivity or alterations in the influence of unidentified neurophysiologic mechanisms that modulate striatal output.