Prenatal exposure of the female chick-embryo Müllerian duct to diethylstilboestrol (DES) decreases its future capacity for epithelial tubular-gland-cell differentiation and oviduct ovalbumin-gene expression. Chick Müllerian ducts after prenatal exposure to different concentrations of DES were tested after birth to determine the response of the oviduct toward the oestrogen induction. The quantity of DNA was biochemically determined, the differentiation of tubular-gland cells in the oviduct was studied by light microscopy, and the expression of the ovalbumin gene was detected by hybridization of the total RNA with radioactive ovalbumin cDNA. Comparisons among these three parameters revealed that the expression of the ovalbumin gene was affected most by DES exposure. Exposure to high doses of DES suppressed ovalbumin-gene expression by 75-78%, and inhibited tubular-gland-cell differentiation and thus decreased the DNA content by 29 and 32% respectively. Exposure to low doses of DES caused suppression of ovalbumin-gene expression by 47-53%, but it did not affect the other two parameters. Prenatal DES exposure has strong inhibitory effects on the Müllerian duct at the age (5-8-day-old embryos) when the organ is undifferentiated. Less inhibition is observed when the organ becomes differentiated (15-day-old embryos and older).