The Jonah genes are expressed twice in development: Jonah RNA is detected during all larval stages, disappears at the end of the third larval instar, and then reappears shortly after eclosion, in the adult midgut. Construction and analysis of Jonah cDNA clones reveals that multiple Jonah genes are transcribed; cDNA clones deriving from at least four different clusters of Jonah genes have been identified. In at least one case, multiple genes in a cluster are transcribed, and one cluster is found to be transcribed both in larvae and adults. Evidence that different Jonah genes are under different control with respect to both spatial and temporal patterns of expression has been provided. Jonah RNA encodes a 28-kDa translation product or products for which we consider a possible function. Jonah RNA of constant length is found to be conserved in all strains of Drosophila melanogaster examined, Jonah genes are found at a minimum of three common chromosomal sites in all of seven D. melanogaster strains examined, and multiple Jonah genes are found in other Drosophila species.