Variant Hepatocyte Nuclear Factor 1 (vHNF1/HNF1beta) is a homeodomain-containing transcription factor first expressed in the primitive endoderm and its derivatives, the visceral and parietal endoderm. It is subsequently expressed in epithelial cells of different organs, including the primitive gut and derivatives (liver, pancreas, lung), the kidney, and transiently, in the neural tube. We report here new data concerning vHnf1 expression in the mouse genital tract, using both RNA analyses and our vHnf1 heterozygous mutant mouse line, in which the first coding exon of the vHnf1 gene is replaced by the NLSLacZ reporter gene. Both beta-galactosidase activity and vHnf1 transcripts are detected in epididymus, vas deferens, seminal vesicle, prostate, uterus and oviduct. RNA analysis and in situ hybridization studies demonstrate that vHnf1 transcripts are restricted to the germinal cells of the testis. Unexpectedly, no beta-galactosidase activity is detected in the testis. We further show that, in addition to the somatic transcript, two more abundant vHnf1 transcript variants, which lack exons 1-4, appear in this organ after meiosis.