The spatial pattern of expression of the murine homeo box-containing gene Hox 1.5 was studied during embryogenesis. In situ hybridization of single-stranded RNA probes to mouse embryo sections revealed a specific spatial distribution of the Hox 1.5 transcripts in mouse embryos 8.5 to 12.5 days postcoitum (p.c.). Analysis of mouse embryos 8.5 days p.c. showed that the gene is expressed in a spatially restricted manner. Expression appears to be limited to the central nervous system with an anterior boundary in the hindbrain and extending posteriorly through caudal regions of the spinal cord. The same spatial pattern of expression was observed in embryos 9.5 to 12.5 days p.c. These results show that the murine Hox 1.5 gene is expressed in a spatially restricted manner during embryonic development similar to the patterns observed in Drosophila homeotic genes.