We have previously characterized an androgen-inducible secretory protein from the mouse vas deferens (MVDP), and a cDNA to its mRNA has been obtained. This report describes altered MVDP gene expression after neonatal exposure to oestrogens. As shown by immunohistochemistry and Western blot analysis, MVDP was missing in the vas deferens from adult mice neonatally exposed to oestrogens. Northern blot analysis showed that the expression of MVDP mRNA was also suppressed. Exogenous testosterone was unable to stimulate MVDP production (either message or protein) in neonatally oestrogenized males. The results suggest that the alterations in gene expression in the oestrogen-exposed vas deferens reflect changes in the programme of differentiation of the organ itself.