Tissue distribution and localization of RNAs from the Xeb1 homoeo-box-containing gene were monitored with Northern blots and in situ hybridization. Xeb1 transcript distribution in larval stage embryos was established by blotting RNAs extracted from microdissected embryos. Those transcripts are restricted to a limited number of embryonic regions such as the dorsal trunk. The tissue/cell localization of Xeb1 transcripts was then monitored at several embryonic stages with in situ hybridization methods using [35S]RNA probes. These homoeo-box transcripts accumulated in a progressive and dynamic fashion. First localized in late gastrulae, they are distributed along the neural tube and in caudal mesoderm at later stages. By the swimming tadpole stage the spatial distribution of the homoeo-box transcripts is limited to specific regions of the central nervous system. Adult spinal cord shows the signal in specific neurons in the ventrolateral field of the gray matter.