During the last few years several loci have been linked to Mendelian forms of Parkinson's disease (PD). To date, 5 causative genes of 10 identified loci are known, and they have provided enormous insight into the molecular pathways involved in this common neurodegenerative disorder. One of the recently identified loci, PARK8, causes autosomal dominant PD with, apparently, various degrees of abnormal deposition of alpha-synuclein or tau in the neuronal cells in the pedigrees currently reported. We genetically characterized four Basque families and found evidence for linkage of autosomal dominant PD to the PARK8 locus, with a maximum 2-point logarithm of odds score of 3.21 (theta = 0.00) for marker D12S345. The clinical features of these families are those of typical PD, including good response to levodopa therapy, rigidity, and akinesia, and a mean age of 55 years at disease onset.