['The inositol 1,4,5-trisphosphate (IP3) receptor is an intracellular calcium channel that couples cell membrane receptors, via the second messenger IP3, to calcium signal transduction pathways within many types of cells. IP3 receptor function has been implicated in development, but the physiological processes affected by its function have yet to be elucidated. In order to identify these processes, we generated mutants in the IP3 receptor gene (itpr) of Drosophila and studied their phenotype during development.', 'All itpr mutant alleles were lethal. Lethality occurred primarily during the larval stages and was preceded by delayed moulting. Insect moulting occurs in response to the periodic release of the steroid hormone ecdysone which, in Drosophila, is synthesized and secreted by the ring gland. The observation of delayed moulting in the mutants, coupled with the expression of the IP3 receptor in the larval ring gland led us to examine the effect of the itpr alleles on ecdysone levels. On feeding ecdysone to mutant larvae, a partial rescue of the itpr phenotype was observed. In order to assess ecdysone levels at all larval stages, we examined transcripts of an ecdysone-inducible gene, E74; these transcripts were downregulated in larvae expressing each of the itpr alleles.'] Does disruption of the IP3 receptor gene of Drosophila affect larval metamorphosis and ecdysone release?