Idiopathic Parkinson's disease defines a group of Parkinson's disease (PD) of which the aetiology is unknown but an underlying brain disease is suspected. We selected patients of this subgroup of PD and investigated the seropositivity rate for anti-Toxoplasma IgG antibody by Sabin-Feldman dye test (SFDT). By measuring seropositivity in PD patients, we searched for a probable relationship between Toxoplasma gondii infection and idiopathic PD incidence. Fifty patients diagnosed with idiopathic PD and 50 healthy volunteers were included in the study. Blood samples were taken from all 100 participants and anti-T. gondii antibody titres were investigated using SFDT. Anti-T. gondii antibodies were detected at a titre of >or=1/16 in 25 of the 50 patients (50%) and in 20 of the control group (40%). No higher antibody titre was found in the control group. In conclusion, despite the emerging literature on a possible relationship between T. gondii infection and neurological disease, and the high anti-T. gondii seropositivity found in our PD patients, we did not detect any statistically significant association between T. gondii and idiopathic PD.