In Drosophila melanogaster, fluctuations in 20-hydroxyecdysone (ecdysone) titer coordinate gene expression, cell death, and morphogenesis during metamorphosis. Our previous studies have supported the hypothesis that betaFTZ-F1 (an orphan nuclear receptor) provides specific genes with the competence to be induced by ecdysone at the appropriate time, thus directing key developmental events at the prepupal-pupal transition. We are examining the role of betaFTZ-F1 in morphogenesis. We have made a detailed study of morphogenetic events during metamorphosis in control and betaFTZ-F1 mutant animals. We show that leg development in betaFTZ-F1 mutants proceeds normally until the prepupal-pupal transition, when final leg elongation is delayed by several hours and significantly reduced in the mutants. We also show that betaFTZ-F1 mutants fail to fully extend their wings and to shorten their bodies at the prepupal-pupal transition. We find that betaFTZ-F1 mutants are unable to properly perform the muscle contractions that drive these processes. Several defects can be rescued by subjecting the mutants to a drop in pressure during the normal time of the prepupal-pupal transition. Our findings indicate that betaFTZ-F1 directs the muscle contraction events that drive the major morphogenetic processes during the prepupal-pupal transition in Drosophila.