ProtRepeatsDB is a database of different types of amino acid repeats in protein sequences belonging to different organisms, integrated with various protein repeats analysis tools. Each of the sub sections of different types of repeats may be browsed by entering different search terms, including RefSeq ID, organism name, keywords, Gene Ontology (GO), repeat size, frequency or regular expression. The comparative search tool compares amino acid repeats amongst multiple organisms. The resource also contains a collection of other related tools, including tools to find different types of repeats and BLAST tool to compare sequences with ProtRepeatsDB repeats.