PARK8 is the most common form of familial Parkinson's disease (PD). We measured biopterin and monoamine metabolite levels in the cerebrospinal fluids of 7 PARK8 patients (I2020T mutation in leucine-rich repeat kinase 2), 2 asymptomatic mutation carriers, and 21 sporadic PD patients. The biopterin levels in PARK8 patients were significantly higher than those in sporadic PD patients, although the symptoms were comparable in both groups, suggesting that PARK8 patients exhibit parkinsonian symptoms with higher biopterin levels than sporadic PD patients.