Competence is an active state that defines the way in which cells respond to an inductive signal. A challenge of developmental biology is to explain not just the nature of the signalling molecules that promote cell specification or differentiation, but also how cells acquire competence to respond to these signals and what that reflects in molecular terms. A recent paper by Carmena et al.(1) has revealed how several signalling mechanisms are used sequentially and in specific combinations to specify two mesodermal (...) lineages in Drosophila. BioEssays 21:455–458, 1999. © 1999 John Wiley & Sons, Inc. (shrink)