Motor fluctuations and non-response to carbidopa-levodopa (Sinemet) therapy are major problems in the long-term management of Parkinson's disease. Levodopa manipulation, addition of adjuvants, and drug holidays are often unsuccessful. Others have shown that the clinical state of stabilized Parkinsonians can be reversed with intravenous administration of large neutral amino acids. Reasoning that dietary protein might precipitate motor oscillations and non-response, a low-protein daytime diet (7 g) was offered to fifteen patients. Eighty-six percent of this sample demonstrated immediate sensitivity to Sinemet. While on a low-protein diet, patients' clinical function was predominantly choreatic. Eight patients required a 10-60 percent reduction in their daily levodopa dose in order to minimize this choreatic tendency. Discontinuation of adjuvants did not compromise motor independence. Conversely, while on a high-protein diet (160 g), patients were predominantly immobile with markedly elevated plasma amino acid and levodopa levels. Consequently, elimination of dietary protein from breakfast and lunch can offer an effective and easily modified method for the amelioration of motor fluctuations and non-response to Sinemet in Parkinson's disease during working hours.