Machado-Joseph disease (MJD) is an autosomal dominant neurodegenerative disorder of late onset, caused by the expansion of a (CAG)n tract in the MJD1 gene. Using BLAST2 sequences between known cDNA variants transcribed by the MJD1 gene and a clone of human genomic DNA, six possible unknown intragenic single-nucleotide polymorphisms (SNPs), at variable positions in the MJD1 gene, were identified. To confirm this, we studied a Portuguese control population, using polymerase chain reaction amplification and single-strand conformation polymorphism analysis for each potential SNP. For four of the possible polymorphisms there was no variability in our population, but the existence of three novel polymorphisms was confirmed: GTT527/GTC527, C1178/A1178, and A1294/ G1294. The polymorphism GTT527/GTC527 (Val/ Val) is located in the coding region, whereas C1178/A1178 and A1294/G1294 are located in the 3'noncoding region of cDNA variants of the MJD1 gene, MJD2-1 and MJD1-1, respectively. All these novel SNPs are in Hardy-Weinberg equilibrium. These intragenic polymorphisms can be useful for (1) the study of the origin of the MJD mutation(s), (2) the study of recombination events, (3) distinction of chromosomes with alleles of identical (CAG)n size in genetic tests (homoallelism), (4) the study of genetic modifiers in the region flanking the MJD1 gene, and (5) association studies in other diseases.