Provides integrated single nucleotide polymorphism (SNP) information about Human Chromosome 21 genes. The Human Chromosome 21 SNP database has integrated SMART database and Entrez dbSNP. The database can be explored through the following tools. The Human Chromosome 21 SNP Quest allows users to see SNP information based on gene name, SNP type, SMART Domain, SNP validate status. Users can also view Human Chromosome 21 SNP Summary Table which contains the summary information about the Human Chromosome 21 genes that contains SNP. Finally, Human Chromosome 21 SNP Detail Table contains the gene, SNP type, SMART domain information about the Human Chromosome 21 genes that contain SNP with SNP type as nonsense, frameshift or non-synonymous, non-conservative in a SMART Domain. The data displayed in the Human Chromosome 21 SNP Database are freely available to general public.