The changes of DNA synthesis as well as the alterations of DNA polymerase alpha and beta have been determined in oviducts from immature (35 days old), mature (about 300 days old) and senescent (about 3 years old) quails in response to diethylstilbestrol (DES). The DNA synthesis in oviducts from immature quails is strongly stimulated by DES; after 12 days, values equivalent to those determined in mature and senescent animals are reached. The DNA synthesis in immature oviducts can be reversibly blocked by progesterone administration; no influence is observed in the case of DNA synthesis in mature as well as senescent animals. During DNA synthesis in immature oviducts, stimulated with DES, DNA polymerase alpha is strongly induced. Co-administration of progesterone blocks this enzyme induction in a reversible and strong way. The activity of DNA polymerase alpha is identical in mature and in immature animals (after DES treatment for 15 days); the activity of the same enzyme in senescent animals is about 40% lower than the values found in the younger quails. The activity of DNA polymerase beta is not altered if the animals are treated with DES or with DES and progersterone; however, the basic level of the enzyme in senescent animals in 50% lower than in immature or in mature animals.