ARB is a software environment for sequence data. It was initiated over 10 years ago and includes a variety of software tools for sequence database maintenance and analysis, controlled by a common graphical user interface. Originally designed for ribosomal RNA data, it can be used for any nucleic and amino acid sequence data. A central database stores processed (aligned) primary structure data, and additional descriptive data can be stored in database fields or linked via networks. A phylogenetic tree visualized in the main window can be used for data access and visualization. The package includes tools for data import/export, sequence alignment, primary and secondary structure editing, profile and filter calculation, phylogenetic analysis, probe design, and other data analysis components. It is used by numerous working groups worldwide. The ARB project was established as an interdisciplinary initiative by the Lehrstuhl für Mikrobiologie and Lehrstuhl für Rechnertechnik und Rechnerorganisation at the Technical University of Munich. It aims to maintain a structured integrative secondary database combining processed primary structures and additional data, and to provide a comprehensive selection of software tools interacting with one another and the central database via a common graphical interface. Software and rRNA databases are publicly accessible. The ARB software is developed for UNIX systems and their derivatives, using C++, C, Perl, and other script languages. It integrates external software tools like GDE and PHYLIP, and includes tools for maximum-likelihood-based phylogenetic analysis. The central database stores sequences representing organisms, genes, or gene products, with unique identifiers. Additional data can be assigned to sequence entries and stored in database fields. The database is hierarchically structured, and data can be customized according to user preferences. The ARB main window allows visualization of phylogenetic trees and database fields. A powerful search tool enables simple and complex searches in database fields. The sequence editor allows visualization and modification of sequence data, with options for color coding and keyboard customization. The secondary structure editor checks for secondary structure in rRNA data. Profiles, masks, and filters are important for sequence data analysis, especially for phylogenetic inference. The ARB positional tree server allows rapid finding of sequence identity or peculiarity, serving as a central tool for fast search of closest relatives for automated sequence alignment or to define diagnostic sequence stretches for primer and probe design. The ARB fast aligner is used for integrating new sequences into existing databases. For protein coding sequences, the alignment is optimized on the amino acid level. The ARB probe design and evaluation tools search the PT server for diagnostic sequence stretches. The ARB multiprobe software component determines sets of up to five probes optimally identifying the target group. Data import and export are supported in commonly used flat file formats. The ARB package provides a comprehensive set of tools for sequence data analysis, with availability and documentation provided on the ARB website. The ARB software is used on various systems, including Linux, Sun SolarARB is a software environment for sequence data. It was initiated over 10 years ago and includes a variety of software tools for sequence database maintenance and analysis, controlled by a common graphical user interface. Originally designed for ribosomal RNA data, it can be used for any nucleic and amino acid sequence data. A central database stores processed (aligned) primary structure data, and additional descriptive data can be stored in database fields or linked via networks. A phylogenetic tree visualized in the main window can be used for data access and visualization. The package includes tools for data import/export, sequence alignment, primary and secondary structure editing, profile and filter calculation, phylogenetic analysis, probe design, and other data analysis components. It is used by numerous working groups worldwide. The ARB project was established as an interdisciplinary initiative by the Lehrstuhl für Mikrobiologie and Lehrstuhl für Rechnertechnik und Rechnerorganisation at the Technical University of Munich. It aims to maintain a structured integrative secondary database combining processed primary structures and additional data, and to provide a comprehensive selection of software tools interacting with one another and the central database via a common graphical interface. Software and rRNA databases are publicly accessible. The ARB software is developed for UNIX systems and their derivatives, using C++, C, Perl, and other script languages. It integrates external software tools like GDE and PHYLIP, and includes tools for maximum-likelihood-based phylogenetic analysis. The central database stores sequences representing organisms, genes, or gene products, with unique identifiers. Additional data can be assigned to sequence entries and stored in database fields. The database is hierarchically structured, and data can be customized according to user preferences. The ARB main window allows visualization of phylogenetic trees and database fields. A powerful search tool enables simple and complex searches in database fields. The sequence editor allows visualization and modification of sequence data, with options for color coding and keyboard customization. The secondary structure editor checks for secondary structure in rRNA data. Profiles, masks, and filters are important for sequence data analysis, especially for phylogenetic inference. The ARB positional tree server allows rapid finding of sequence identity or peculiarity, serving as a central tool for fast search of closest relatives for automated sequence alignment or to define diagnostic sequence stretches for primer and probe design. The ARB fast aligner is used for integrating new sequences into existing databases. For protein coding sequences, the alignment is optimized on the amino acid level. The ARB probe design and evaluation tools search the PT server for diagnostic sequence stretches. The ARB multiprobe software component determines sets of up to five probes optimally identifying the target group. Data import and export are supported in commonly used flat file formats. The ARB package provides a comprehensive set of tools for sequence data analysis, with availability and documentation provided on the ARB website. The ARB software is used on various systems, including Linux, Sun Solar