SBASE 2.0 is the second release of SBASE, a collection of annotated protein domain sequences. SBASE entries represent various structural, functional, ligand-binding and topogenic segments of proteins [Pongor, S. et al. (1993) Prot. Eng., in press]. This release contains 34,518 entries provided with standardized names and it is cross-referenced to the major protein and nucleic acid databanks as well as to the PROSITE catalog of protein sequence patterns [Bairoch, A. (1992) Nucl. Acids Res., 20 suppl, 2013-2018]. SBASE can be used for establishing domain homologies using different database-search tools such as FASTA [Lipman and Pearson (1985) Science, 227, 1436-1441], FASTDB [Brutlag et al. (1990) Comp. Appl. Biosci., 6, 237-245] or BLAST3 [Altschul and Lipman (1990) Proc. Natl. Acad. Sci. USA, 87, 5509-5513] which is especially useful in the case of loosely defined domain types for which efficient consensus patterns can not be established. SBASE 2.0 and a set of search and retrieval tools are freely available on request to the authors or by anonymous 'ftp' file transfer from mean value of ftp.icgeb.trieste.it.