From its origin the Protein Information Resource (http://www-nbrf. georgetown.edu/pir/) has supported research on evolution and computational biology by designing and compiling a comprehensive, quality controlled, and well-organized protein sequence database. The database has been produced and updated on a regular schedule since 1984. Since 1988 it has been maintained collaboratively by the PIR-International, an association of data collection centers engaged in international cooperation for the development of this research resource during a period of explosive acquisition of new data. As of June 1997, essentially all sequence entries have been classified into families, allowing the efficient application of methods to propagate and standardize annotation among related sequences. The databases are available through the Internet by the World-Wide Web and FTP, or on CD-ROM and magnetic media.