Oncogenes c- myc , H- ras , c- fos and c- erb - B were constitutively expressed in immature chick oviduct withdrawn from estrogen administration for 2.5 weeks after 10 d of primary estrogen stimulation. Following secondary estrogen stimulation of the withdrawn chicks, synthesis of egg white proteins is rapidly induced and remaining non-functioning tubular gland cells are stimulated to proliferate with a doubling time of 24 h. During first 12 h of secondary estrogen stimulation, H- ras mRNA levels doubled and did not increase further at 24 h and 48 h. The steady state levels of c- myc , erb - B and c- fos mRNA decreased 24 h following secondary estrogen stimulation. The levels of these oncogene RNAs in oviduct were similar at 48 h following secondary estrogen stimulation to those from immature chicks administered 10 d of primary estrogen stimulation. Thus elevated expression of c- myc and c- fos mRNA does not appear to be necessary components for sustained estrogen induced cell proliferation in the chick oviduct.