The uptake, metabolism and subcellular distribution of oestradiol and oestriol in endometrial, myometrial and vaginal tissue of postmenopausal women under physiological conditions were studied by giving 3H-labelled oestradiol or oestriol in subphysiological doses by continuous infusion lasting 12 h before hysterectomy. The three tissues obtained from each woman were separated into three fractions: two cytosol fractions (free oestrogens and specifically bound) and one nuclear fraction. The results show an accumulation of both oestrogens in the target tissues, we found an approximately 33 times higher [3H]E2 concentration in endometrium (dpm per g) than in plasma (dpm/ml), 20 times in myometrium and 10 times in vaginal tissue. After the E3 infusions the tissue/plasma gradient was 37 for endometrium, 19 for myometrium and 11 for vagina. In plasma and tissues a metabolite of E3 could tentatively be identified as 16 alpha-hydroxyoestrone. The subcellular distribution showed that 60-80% of E2 and E3 is accumulated in the nuclear fraction of all tissues studied, no nuclear bound oestrone could be detected. From these results the conclusion was drawn that oestradiol still is the major tissue oestrogen in postmenopausal women and that it is mainly nuclear bound. Endometrium of postmenopausal women accumulates higher concentrations of E2 and E3 than vaginal tissue from the same individual, no preferential uptake of oestriol occurs under physiological conditions.