An integrated database for the eastern North American monarch butterfly (Danaus plexippus). MonarchBase provides access to a wide-range of genomic, proteomic, and related biological information. Moreover, MonarchBase provides access to an updated version of genome assembly (v3) upon which all data integration is based. These include genes with systematic annotation, as well as other molecular resources, such as brain expressed sequence tags, migration expression profiles and microRNAs. MonarchBase utilizes a variety of retrieving methods to access data conveniently and for integrating biological interpretations.