The sites described earlier we believed were fairly representative of the repositories available to researchers. Our literature search indicated that other sites are available. SigPath is described by Campagne et al. [16] as an information management system that stores both quantitative information on cellular components and their interactions, and the basic reactions governing those interactions; EcoCyc, which is described as a comprehensive database resource for Escherichia coli by Keseler et al. [17] ; JWS Online, described by Olivier and Snoep as a repository of kinetic models describing biological systems that can be interactively run and interrogated over the Internet [18] ; and the Database of Quantitative Cellular Signaling, which Sivakumaran et al. describe as a repository of models of signaling pathways [19] .