text: The eFS assay could be used to analyze other cell or tissue types. By assessing enrichment in GFP-expressing CD2-negative as well as CD2-positive cells, and by crossing a common pool of reporter transformant male flies to females expressing CD2 in different cell types, it is possible to assay specificity as well as activity. Accelerating the annotation of the regulatory genome in Drosophila should in principle generate the kind of large-scale regulatory interaction data that would allow exploring the network properties of transcriptional regulation.