Estrogen actions are mainly mediated by estrogen receptor (ER)alpha and ERbeta which in turn are regulated by several factors including age, sex and gonadal steroid hormones 17beta-estradiol and testosterone. In the present study, we have used nuclear run-off assay to examine the effect of these factors on the rate of transcription of ERalpha and ERbeta of mouse cerebral cortex. The run-off assay result was further corroborated with the measurement of steady state level of ERalpha and ERbeta mRNA by semiquantitative RT-PCR method. Our results reveal that ERalpha transcription rate decreases in old mice of both sexes, whereas ERbeta transcription rate decreases only in old females when compared to their adult counterparts. 17beta-Estradiol supplementation reduces the transcription rate of ERalpha and ERbeta in all groups except in adult male while testosterone treatment down regulates the transcription rate of ERalpha and ERbeta in all groups. The semiquantitative RT-PCR analysis reveals that the level of ERalpha mRNA decreases in old male but shows no effect in old female as compared to adult counterpart. In contrast, ERbeta transcript level decreases in old mice of both sexes. Furthermore, ERalpha mRNA level is higher in adult female than in adult male but no sex-dependent difference is seen in ERbeta mRNA level. Supplementation of 17beta-estradiol shows no significant alteration but testosterone reduces the ERalpha level in male mice, while 17beta-estradiol and testosterone down regulate the ERalpha level in female mice of both ages. In case of ERbeta, 17beta-estradiol decreases the transcript level in all groups except adult male while testosterone treatment results in the down regulation of transcript level in all groups. Thus these findings suggest differential effects of age, sex, 17beta-estradiol and testosterone supplementation on the transcription of mouse ER genes which may account for differences in the protein levels of ERalpha and ERbeta and their functions in the brain.