Motivation: Multiple alignments of protein sequences are the basis of structural and functional analysis of protein families. It is however difficult even for an expert biologist to comprehend an alignment of more than 50 to 100 homologous sequences.
Results: This paper presents a browser for the analysis of multiple alignments of large numbers of protein sequences. Phylogenetic trees and consensus sequences are computed and used to summarise the alignments; these data are stored in a structure called Rich Family Description. Summary alignments and trees are displayed in HTML pages and can be developed or reduced by the user. This browser is used to display the ProDom domain families on the Web. Its zooming facilities allow extracting information from alignments of more than 1000 homologous sequences.