Spinocerebellar ataxia type 1 (SCA 1) is an autosomal dominant disorder characterized by neurodegeneration of the cerebellum, spinal cord and brainstem. This neurodegeneration disease is associated with expansion of unstable CAG repeats within the coding region of the gene. We are conducting a local survey of the normal population and candidate patients to analyze the CAG repeats in SCA 1 gene. So far, we have collected peripheral blood from 78 normal individuals and 10 patients with dominant inherited ataxia disorders, and assayed the SCA1 CAG trinucleotide repeat using genomic polymerase chain reaction (PCR). Even though no local SCA 1 patients have been identified, we have established the distributions of the CAG repeat units of SCA 1 gene in the normal population in Taiwan. The normal range of CAG repeats is from 22 to 33 repeats, with the most common being 30 repeats. The range is relatively narrow compared to that reported for other ethnic groups. In addition, direct genomic PCR analysis of the SCA 1 gene from villous DNA has been successful in our laboratory. Screening of SCA 1 patients from patients with dominant inherited ataxia is currently underway in our laboratory. Here, we demonstrate that our molecular analysis technique makes possible the quick and accurate diagnosis of SCA1 patients and prenatal screening for SCA 1 families.