Within folded strands of a protein, amino acids (AAs) on every adjacent two strands form a pair of AAs. To explore the interactions between strands in a protein sheet structure, we have established an Internet-accessible relational database named SheetsPairs based on SQL Server 2000. The database has collected AAs pairs in proteins with detailed information. Furthermore, it utilizes a non-freetext database structure to store protein sequences and a specific database table with a unique number to store strands, which provides more searching options and rapid and accurate access to data queries. An IIS web server has been set up for data retrieval through a custom web interface, which enables complex data queries. Also searchable are parallel or anti-parallel folded strands and the list of strands in a specified protein.