Our current knowledge of mammalian forebrain development is meagre. The comparatively few relevant anatomical landmarks are, however, being supplemented by gene expression studies which are able to identify subsets of anatomical structures. We previously described cloning, subchromosomal localization and preliminary structural characterization of the human WNT8B gene, the first mammalian Wnt8b gene to be reported. Wnt genes encode intercellular signalling molecules which play a variety of critical roles in early development, including, in several cases, a presumed role in brain development. In the current report we present the full-length cDNA sequence and genomic organization of the human Wnt8b gene and report studies of expression of the Wnt8b gene in human and mouse embryos. The human and mouse expression patterns appeared identical and were restricted to the developing brain, with the great majority of expression being found in the developing forebrain. In the latter case expression was confined to the germinative neuroepithelium of three sharply delimited regions: the dorsomedial wall of the telencephalic ventricles (which includes the developing hippocampus), a discrete region of the dorsal thalamus and the mammillary and retromammillary regions of the posterior hypothalamus. Expression in the developing hippocampus may suggest a role for WNT8B in patterning of this region and subchromosomal localization of the human gene to 10q24 may suggest it as a candidate gene for partial epilepsy in families where the disease has been linked to markers in this region.