Two hormones, 20-hydroxyecdysone (20E) and juvenile hormone (JH) are key regulators of insect development including the differentiation of the alternative caste phenotypes of social insects. In addition, JH plays a different role in adult honey bees, acting as a ‘behavioural pacemaker’. The functional receptor for 20E is a heterodimer consisting of the ecdysone receptor and ultraspiracle (USP) whereas the identity of the JH receptor remains unknown. We have cloned and sequenced a cDNA encoding Apis mellifera ultraspiracle (AMUSP) and examined its responses to JH. A rapid, but transient up-regulation of the AMUSP messenger is observed in the fat bodies of both queens and workers. AMusp appears to be a single copy gene that produces two transcripts (∼4 and ∼5 kb) that are differentially expressed in the animal's body. The predicted AMUSP protein shows greater sequence similarity to its orthologues from the vertebrate–crab–tick–locust group than to the dipteran–lepidopteran group. These characteristics and the rapid up-regulation by JH suggest that some of the USP functions in the honey bee may depend on ligand binding.