Ontogeny and cellular localization of the lutropin receptor (LH-R) mRNA were studied in fowl gonads between day 5 of incubation and day 1 of posthatch. In situ hybridization using an antisense cRNA probe demonstrated that LH-R gene expression began at embryonic day 7 in females and day 14 in males. In female embryos, the specific hybridization was detected in not only developing left ovaries but also regressing right ovaries. The LH-R mRNA expression in the right ovary was detectable until hatch. LH-R mRNA was localized in the medullary cords in ovaries and interstitial tissues in testes. These results are consistent with previous reports on ontogenic analysis of LH-dependent steroidogenesis in chicken embryo gonads.