HNF1 (Hepatic Nuclear Factor 1) and vHNF1 are transcriptional regulators containing a highly divergent homeodomain. The first was initially found in liver nuclear extracts and is crucial for the transcription of albumin and many other hepatocyte specific genes, while the second was found in dedifferentiated hepatoma cells. Both recognize the same DNA binding site and can form homo and heterodimers in vitro and in vivo. In situ hybridization analyses have been performed to delineate the spatial and temporal pattern of expression of vHNF1 relative to HNF1 during mouse embryogenesis. The results show that accumulation of vHNF1 mRNAs expression is detected in several tissues of the embryo of both endodermal and mesodermal origin. Expression occurs in the yolk sac, the primitive gut, the liver primordium, and at different stages of kidney development in polarized epithelial structures and usually precedes that of HNF1. vHNF1 expression seems particularly prevalent with morphogenetic events in the kidney and may be a marker for certain polarized epithelium.