Summary: The Biological Biochemical Image Database is a WWW accessible relational database of archived images from research articles that describe regulatory pathways of higher eukaryotes. Pathway information is annotated and can be queried in the study of complex gene expression. In this way, complex regulatory pathways can be tested empirically in an efficient manner in the context of large-scale gene-expression systems. Availability: http://bbid.grc.nia.nih.gov Contact: beckerk@grc.nia.nih.gov