The Ribosomal Database Project (RDP) is a curated database that provides ribosome-related data, analysis services, and associated computer programs. It includes phylogenetically ordered alignments of ribosomal RNA (rRNA) sequences, derived phylogenetic trees, rRNA secondary structure diagrams, and various software for handling, analyzing, and displaying alignments and trees. The data are available via anonymous FTP, electronic mail, gopher, and WWW. The electronic mail and WWW servers provide ribosomal probe checking, approximate phylogenetic placement of user-submitted sequences, screening for possible chimeric rRNA sequences, automated alignment, and a suggested placement of an unknown sequence on an existing phylogenetic tree. The RDP provides data, programs, and services related to the ribosome. This paper describes changes introduced since last year's description. Details about currently available analysis functions, data, and available programs can be found on the servers described below. The ribosomal RNA sequences in the RDP alignments are drawn from major sequence repositories and direct submissions to the RDP. During the past year, RDP staff extended extensive effort to obtaining and examining all publications related to the sequencing of small subunit ribosomal RNA. Bibliographic citations from the sequence databases were updated from 'Unpublished' when possible and corrected when found to be in error. In each instance it was confirmed that (i) the published paper referred to the given public database sequence and (ii) the feature annotations were consistent with the published paper. More than 800 small subunit (SSU) rRNA sequences have been added to the prokaryotic alignment, bringing the total to over 3600. The eukaryotic alignment has been extensively reworked, and several hundred new sequences added as well. New this year is an alignment of ~1000 small subunit mitochondrial sequences. The full molecular length ranges from 611 bp for Trypanosoma brucei to 2023 bp for Lupinus luteus representing a tremendous amount of variation among organisms. Phylogenetic trees are available for the sequences in the posted prokaryotic, eukaryotic and mitochondrial SSU rRNA alignments. They have been built by sequential addition of sequences to starting trees of full-length sequences, all using a maximum-likelihood criterion. The RDP also offers a collection of SSU and LSU rRNA secondary structure diagrams in PostScript format generated and supplied by R. Gutell and his collaborators. All of the RDP data and analysis services can be accessed through the RDP World Wide Web server: http://rdpwww.life.uiuc.edu/. The Web pages have been extensively revised. The RDP automated electronic mail server also provides both data and analysis services. Its address is server@rdp.life.uiuc.edu. The RDP data can be accessed via anonymous FTP to rdp.life.uiuc.edu. The RDP gopher hostThe Ribosomal Database Project (RDP) is a curated database that provides ribosome-related data, analysis services, and associated computer programs. It includes phylogenetically ordered alignments of ribosomal RNA (rRNA) sequences, derived phylogenetic trees, rRNA secondary structure diagrams, and various software for handling, analyzing, and displaying alignments and trees. The data are available via anonymous FTP, electronic mail, gopher, and WWW. The electronic mail and WWW servers provide ribosomal probe checking, approximate phylogenetic placement of user-submitted sequences, screening for possible chimeric rRNA sequences, automated alignment, and a suggested placement of an unknown sequence on an existing phylogenetic tree. The RDP provides data, programs, and services related to the ribosome. This paper describes changes introduced since last year's description. Details about currently available analysis functions, data, and available programs can be found on the servers described below. The ribosomal RNA sequences in the RDP alignments are drawn from major sequence repositories and direct submissions to the RDP. During the past year, RDP staff extended extensive effort to obtaining and examining all publications related to the sequencing of small subunit ribosomal RNA. Bibliographic citations from the sequence databases were updated from 'Unpublished' when possible and corrected when found to be in error. In each instance it was confirmed that (i) the published paper referred to the given public database sequence and (ii) the feature annotations were consistent with the published paper. More than 800 small subunit (SSU) rRNA sequences have been added to the prokaryotic alignment, bringing the total to over 3600. The eukaryotic alignment has been extensively reworked, and several hundred new sequences added as well. New this year is an alignment of ~1000 small subunit mitochondrial sequences. The full molecular length ranges from 611 bp for Trypanosoma brucei to 2023 bp for Lupinus luteus representing a tremendous amount of variation among organisms. Phylogenetic trees are available for the sequences in the posted prokaryotic, eukaryotic and mitochondrial SSU rRNA alignments. They have been built by sequential addition of sequences to starting trees of full-length sequences, all using a maximum-likelihood criterion. The RDP also offers a collection of SSU and LSU rRNA secondary structure diagrams in PostScript format generated and supplied by R. Gutell and his collaborators. All of the RDP data and analysis services can be accessed through the RDP World Wide Web server: http://rdpwww.life.uiuc.edu/. The Web pages have been extensively revised. The RDP automated electronic mail server also provides both data and analysis services. Its address is server@rdp.life.uiuc.edu. The RDP data can be accessed via anonymous FTP to rdp.life.uiuc.edu. The RDP gopher host