We have investigated the expression of the retinoid X receptor-␣ (RXR␣) gene in the developing chicken embryo by using nonradioactive wholemount in situ hybridization. At the earliest stage of development examined (stage 9; J. Morphol. 88:49-92), we detect RXR␣ transcripts in a stretch of neuroepithelium corresponding roughly to the presumptive caudal hindbrain. Upon formation of the rhombomeres at stage 12, a strongly RXR␣-positive region extends from a sharp rostral limit at the boundary between rhombomeres 6 and 7 caudad to at least the level of somite 9. This pattern of highest expression continues at least until stage 22 but with some variability in the caudal extent. A lower level of expression extends throughout the spinal cord. Transverse sections show that RXR␣ transcripts are expressed in a gradient, with the highest levels near the roof plate and decreasing toward the floor plate. At later stages, the level of expression is highest in the proliferative ventricular zone. However, at reduced levels, RXR␣ transcripts are also detectable in the mantle zone as well as outside the developing central nervous system, for example, in the neural crest and the limb buds. Nine-cis-retinoic acid up-regulates RXR␣ transcripts at stages 19.5-22.0 within a few hours, augmenting but not expanding the expression pattern. Northern blots demonstrate the potential expression of multiple RXR␣ isoforms in the central nervous system at posthatch stages. These results implicate the RXR␣ receptor in both rostrocaudal and transverse patterning of the neural tube.