A number of neurodegenerative diseases including Parkinson's disease (PD) have been shown to be associated with polymorphic variants of mitochondrial DNA. The A4336G mutation in the tRNA(Gln) gene was reported to occur at a higher frequency in individuals with Parkinson's disease and Alzheimer's disease (AD) than in age-matched controls. Similarly, we recently noted an elevated frequency of alterations at positions 15927 and 15928 in the tRNA(Thr) gene, resulting in the loss of a HpaII site, in patients suffering from multiple sclerosis (MS) with severe optic involvement. Here we report on the result of screening 100 PD patients and 100 age- and sex-matched controls for the presence of the A4336G mutation and the loss of the HpaII site in the tRNA(Thr) gene. Our result shows that loss of the HpaII site is significantly more frequent in patients than in controls. In contrast, we were not able to detect a difference in the frequency of the A4336G mutation in the tRNA(Gln) gene between patients and controls.