Abstract: The World-Wide Web server of the PBIL (Pole Bioinformatique Lyonnais) provides an on-line access to sequence databanks as well to many tools devoted to nucleic and protein sequences analyses. This server allows to query nucleotide sequence banks in EMBL and GenBank formats and protein sequence banks in the SWISS-PROT and PIR format. The query engine on which is based our data banks access is the ACNUC system. It allows the possibility to build complex queries to access functional zones of biological interest and to retrieve large sets of sequences. Of special interest are the unique features provided by this system to query the gene families data banks developed at the PBIL. The server also provides access to a wide range of sequence analyses methods: similarity search programs, multiple alignments, protein structure prediction and multivariate statistics. But what makes the originality of this server is in fact the integration of these two aspects: sequence retrieval and sequence analysis. Indeed, thanks to the introduction of re-usable lists, it is possible to perform treatments on large sets of data instead of single sequences. The PBIL server can be reached at: http://pbil.univ-lyon1.fr.