Complex biological regulatory pathways of higher eukaryotes are poorly described, difficult to present and difficult to study. One reason for this is a lack of a central repository for regulatory pathway information. The Biological Biochemical Image Database (BBID) is a World-Wide Web searchable database of images from research articles that describe regulatory pathways of higher eukaryotes. These images are not redrawn, were obtained with permission, are referenced and are thus attributable back to the original journal and authors. The elements of each image are loaded into a table that can be searched by keywords including: gene name, cell/tissue type, species etc. In parallel, these image elements are attached to the gene files that underlie large-scale gene expression studies such as cDNA microarrays. Pathway information for complex gene expression studies can then be extracted automatically. In this way, complex regulatory pathways can be tested empirically in an efficient manner in the context of large-scale gene expression systems. The BBID can be accessed at the following address http://www.grc.nia.nih.gov/hd/bbid99.htm.