Neuroleptic malignant syndrome (NMS) is induced by alteration of medication in Parkinson's disease (PD); and blood coagulation disorder is regarded as one of the mechanisms implicated in NMS. We have studied markers of blood coagulation and fibrinolysis in 270 patients with PD and 159 healthy controls matched in age and gender. The average values of prothrombin time (international normalized ratio) and plasma levels of prothrombin fragment(1+2), D-dimer, plasmin-alpha 2 antiplasmin complex, thrombomodulin and E-selectin were higher in patients receiving antiparkinsonian agents as compared to the patients without any medication or healthy controls. The effect of antiparkinsonian drugs was analyzed by dividing the patients into three groups according to the medication: the patients under the combination therapy with levodopa and a dopamine agonist, the patients administered levodopa, and those that received a dopamine agonist. Of the three groups, the patients under the combination therapy had the highest values of these markers, and those treated with only levodopa had the lowest values. PD patients receiving antiparkinsonian drugs are often associated with blood coagulation abnormalities, and plasma hemostatic markers should be routinely assessed in the management of such patients. Further study is needed to determine whether these abnormalities predispose to the development of NMS.