The physiological responses involved in mediating adaptive change due to varying environmental conditions or social interactions are complex and involve integration of numerous signaling pathways. With Drosophila melanogaster, I can investigate the responses to varied environmental and social stimuli through quantification of signaling activity, stress resistance, and changes in gene expression and behavior. My work focuses on investigating signaling pathways that adult insects use to regulate homeostasis. The steroid hormone 20- hydroxyecdysone (ecdysone) and its receptor (EcR/USP) are vital during arthropod development for coordinating molting and metamorphosis. However, recent adult studies in Drosophila melanogaster indicate that the hormone and receptor influence many processes. I characterized the wild-type expression patterns and activity of ecdysone receptors in individual tissues during early adult life. I found that receptor components EcR and usp were expressed in numerous adult tissues, but receptor activation varied depending on tissue type and adult age. EcR/USP activity did not detectably change in response to environmental stimuli but is reduced when a constitutively inactive ecdysone receptor is present. The current state of our understanding of this signaling system is reviewed with reference to my findings. I discuss future directions focusing on identifying locations of hormone synthesis, metabolism, and storage, isoform-specific roles of EcR, and functional roles of gene repression and activation to link hormone receptor activity with physiological responses. Adult physiology is also regulated by interactions between adipose tissue and the central nervous system. Genes expressed in the insect fat body are involved in regulating nutrient homeostasis, stress resistance, immunity, reproduction, and behavior. Of particular interest is female-specific independent of transformer (fit). Several studies indicate that fat body expression of fit may influence responses to environmental change by altering adult behavior or physiology. Our lab created fit mutants that I used to assess the effects of these mutations on adult Drosophila physiology and behavior. I found that fit mutant adults survive longer without food, have increased nutrient levels, are more active, and feed extensively. My findings indicate that the fat-biased gene fit influences multiple aspects of adult physiology that affect appetite modulation, metabolism, and behavior.