Oestrogens are not exclusive to the female gender but occur in moderate circulating levels of 25-70 pg ml⁻¹ in men, compared to 44-153 pg ml⁻¹ in women. Arising from aromatisation of testosterone (T), oestrogen is considered to have many opposing physiological functions and the progressive T decline in the aging male is associated with relative and/or absolute increase in serum oestradiol (E₂). Sexual disinterest and erectile dysfunction (ED) in the elderly may well be due to pathophysiological E₂-T imbalance; the altered hormonal ratio may also explain the higher incidence of ED in hyperestrogenism or following exposure to environmental/plant oestrogens.