The first two editions of the E. coli Gene-Protein Index were published to provide identifications of protein spots resolved by two-dimensional gel electrophoresis as the products of known genes. This third edition has been expanded to include information about genes and proteins gained directly from two-dimensional gel analysis--including information about protein spots not yet characterized genetically or biochemically--and is therefore more properly called a cellular protein database. An alpha-numeric designation has been uniquely assigned to each of the 616 polypeptide spots in the current database. To this, information is linked about the polypeptide's identification (protein name, gene name, Enzyme Commission--EC number), location on reference gels (x-y coordinates), genetics (Genbank code, DNA sequence reference), biochemistry (molecular weight, isoelectric point), and physiology (steady state level of the protein as a function of media and temperature, membership in various regulons and stimulons).