Aromatase (cytochrome P450 19A1) is responsible for catalyzing the conversion of androgens to estrogens and is expressed in a variety of tissues including ovary, brain, placenta and adipose tissues. Strong biological evidence supports the benefits of estrogen on brain functioning, morphology and also on ovarian function. Although insulin has been shown to stimulate ovarian steroidogenesis and could alter aromatase activity there are few data about the effects of diabetes on aromatase enzyme of brain and gonadal tissues. In this study we investigated the effects of experimental diabetes on aromatase expression in hippocampus, ovary and uterus. Female Sprague-Dawley rats were injected with streptozotocin (45 mg/kg) to induce diabetes. Age-matched non-diabetic rats were used as control. At the end of 8-weeks diethylstilbesterol (0.1 mg/kg, s.c.) was enjected to rats 24 hours before exsanguination for initiating oestrus cycle. After the isolation of hippocampus, ovary and uterus, tissue homogenats were prepared and evaluated for aromatase proteins by western blot. Responses of unilateral uterus tissues of rats to carbachol (10-8-10-4 M) and oxytocin (10-8-10-6 M) were investigated via organ chamber experiments. Aromatase levels were not altered in hippocampal brain extracts but attenuated in ovary and uterus tissue homogenates of diabetic rats compaired to control. Contraction responses induced by both carbachol and oxytocin were decreased in uterus tissues of diabetic rats when studied in vitro. In conclusion, these results indicated for the first time that, aromatase levels were not altered in hippocampus but attenuated in uterus and ovary of 8-weeks experimentally diabetic rats. Uterus contraction responses were also impaired in diabetic rats. * Approved by Hacettepe University Animal Ethics Committee (2006/8-6).