We are developing a signal transduction database which represents molecular interactions involved in the signaling pathways in a cell from the activation of cell surface receptors by external signals to the activation of transcription factors in the nucleus. The database is linked to the Medline literature, the SWISS-PROT and PIR protein sequence database, the PDB protein 3-D structural database, the LIGAND chemical database for enzyme reactions, and the OMIM database on genetic diseases. We provide a graphical user interface of the World Wide Web (WWW) to access this database.