The objective of the present study was to determine the temporal expression of oestrogen receptor alpha in the uterus of the developing bovine fetus. Bovine fetuses were collected and approximate gestational age was determined by crown-rump measurement. Fetal uteri were either snap frozen in dry ice-ethanol, or placed in sterile Dulbecco's modified Eagle's medium. Fetal uteri (n = 20) were homogenized and cytosolic oestrogen receptor measured by [3H]ligand binding assay. Total RNA was extracted from fetal uteri (n = 53) and amplified by reverse transcription-polymerase chain reaction using primers specific for the oestrogen receptor, progesterone receptor, interleukin 1 alpha, interleukin 6, transforming growth factor beta, prolactin receptor, epidermal growth factor receptor, retinoic acid receptor isoforms alpha, beta, and gamma, or glyceraldehyde-3-phosphate dehydrogenase (loading control). Expressed as a ratio with glyceraldehyde-3-phosphate dehydrogenase, mRNA encoding oestrogen receptor was identified in fetal uteri throughout the period from day 65 to day 200, and was increased from day 100 to day 185 (P < 0.003); uterine samples from day 100 to day 200 expressed interleukin 1 alpha, interleukin 6, transforming growth factor beta, prolactin receptor, epidermal growth factor receptor and retinoic acid receptor isoforms alpha, beta, and gamma, but did not express detectable mRNA encoding progesterone receptor. Despite the presence of mRNA encoding oestrogen receptor, [3H]oestradiol binding was not detected until after day 155. Fetal uterine explants collected at days 100-110 (n = 3) or at days 185-200 (n = 3) were cultured in the presence of oestradiol (1.0 nmol l-1, or vehicle); there was a significant effect of oestradiol treatment on specific mRNA expression at days 185-200 (P < 0.014), but not at days 100-110 (P = 0.71). It is concluded that mRNA encoding oestrogen receptor is constitutively expressed at least from day 65 in the uterus of the bovine fetus, but that oestrogen receptor alpha protein and a functional oestrogen response are not present until late in the second third of pregnancy.