The delta opiate receptor gene has been cloned from the mouse neuroblastoma-rat glioma hybrid cell NG108-15. The clone that we isolated is apparently identical to that reported by Evans et al. [Evans, C. J., Keith, D. E., Jr., Morrison, H., Magendzo, K. & Edwards, R. H. (1992) Science 258, 1952-1955] and essentially identical with that of Kieffer et al. [Kieffer, B. L., Befort, K., Gaveriaux-Ruff, C. & Hirth, C. G. (1992) Proc. Natl. Acad. Sci. USA 89, 12048-12052]. We have found full-length transcripts of the gene in mouse brain but in no other tissues examined. Within the brain the gene is expressed at low levels in many regions but transcripts are found in particularly large amounts in the anterior pituitary and pineal glands. Since these tissues are located outside the blood-brain barrier, opioid peptides easily can reach receptors in these areas from the blood. The gene, which is present as a single copy, has been mapped to the distal region of mouse Chromosome 4.