The present study describes the effects of oestradiol-17 beta and diethylstilboestrol (DES) on several oestrogenic responses in the immature rat uterus Diethylstilboestrol was weaker than oestradiol in inducing uterine eosinophilia, water imbibition and mitoses, as strong as oestradiol in eliciting epithelial hypertrophy at 24 h after treatment, and stronger than oestradiol in eliciting the reduction of epithelial cell height at 6 h after treatment and myometrial cell hypertrophy at 24 h after treatment. In addition, differences among the mitotic responses to oestrogen of the different uterine cell types were also detected. The above dissociation of the effects of DES and oestradiol-17 beta is in agreement with the hypothesis that eosinophil-mediated non-genomic responses, genomic responses and cell proliferation are mediated by independent mechanisms, involving different receptors which may have different affinities for both compounds. The eosinopenia and eosinophil degranulation under DES treatment suggest an explanation for the effect of DES on water imbibition. The dissociation among genomic responses from the different uterine cell types supports the hypothesis that different kinds of cytosol-nuclear oestrogen receptors exist.