Understanding developmental processes and building towards integrative systems biology require detailed knowledge of the spatio-temporal expression of genes and proteins. We have developed a software package for collecting, storing and searching the annotation of protein or gene expression patterns in Drosophila melanogaster. Using standard Drosophila anatomy and Gene Ontologies, the system can readily capture expression patterns at any stage of development and in all recognized tissue types as well as details of sub-cellular localization. The web-based system allows multiple groups to work in collaboration and share images and annotation. AVAILABILITY: http://www.flannotator.org.uk/.