The gene-protein database of Escherichia coli has as its core an index that links each of the protein spots from a two-dimensional polyacrylamide gel to the gene that encodes the protein. Additional information about each protein and its gene is generated from two-dimensional gel analysis or collated from the literature to form the database. Earlier editions of the database have provided periodic updates of information. The current edition does this, but also introduces a new reference gel image produced by an electrophoresis system recently adopted in this laboratory. The new gel system was chosen because it offers an improved opportunity for other investigations to produce close replicas of the reference gel pattern, thereby allowing easier access to the information of the database and encouraging independent contribution to the database. The new gel format also is larger and hence more compatible with computer assisted image analysis, which has become essential for a project of this magnitude. This edition continues the use of the former reference gel images, but adds a reference image of an equilibrium gel of E. coli strain W3110 produced by the new standardized gel system. At this time, 55% of the protein spots annotated on the previous equilibrium reference gel for this organism have been located on the new reference image, and these identifications are included in the tables of the database.