The LocusLink and RefSeq databases were initiated to address data-access problems resulting from significant increases in both sequence data and the number of web sites relating information about genes. For example, it is increasingly difficult to identify unambiguously which sequence—of the many publicly available—is an appropriate, complete representative of a given mRNA or protein. Inversely, given an mRNA or protein sequence, it can also be a challenge to determine the official name or symbol for the gene from which the sequence was derived. And once a gene symbol or name is known, identifying other web resources that include information about that gene of interest may be very time-consuming. In its role as a web directory, LocusLink provides a single point-of-access to a variety of gene-specific information sources including web resources and RefSeq. RefSeq provides a non-redundant data set of reference sequences representing transcripts and proteins of known genes. RefSeq records include links to LocusLink, thereby facilitating making connections among sequence data, gene names and related biological information. The LocusLink and RefSeq resources establish reference sequences and stable database identifiers (LocusID) that can be used in variation, mutation and expression analyses.