In 1913, Guggenheim identified L-DOPA in the seedlings, pods, and beans of the broad bean, Vicia faba (VF). Since then, anecdotal cases of symptomatic improvement after VF consumption have been described in patients with PD. In the present study, five healthy volunteers and six PD patients (mean age, 63.5 years; mean disease duration, 13 years; stage III, Hoehn-Yahr scale) ate 250 g cooked VF after 12 hours off medication. Blood samples for L-DOPA measurements (by HPLC-ED) were obtained before eating VF and every 30 minutes, for 4 hours. During this period, a substantial clinical improvement was noted and three patients also showed severe dyskinesias. High plasma L-DOPA values were also measured (Cmax 0.66 to 1.20 micrograms/ml; AUC 1.82 to 4.12 micrograms/ml/H). In addition, their clinical performance and plasma L-DOPA levels were compared to those found after 125 mg L-DOPA + 12.5 mg carbidopa ingested on another day. These data show that VF ingestion produces a substantial increase in L-DOPA plasma levels, which correlates with a substantial improvement in motor performance. Our findings may have implications for the treatment of PD, especially in patients with mild symptoms.