This study examined the effect of age, ovariectomy and dietary phytoestrogen ingestion on 17-߭estradiol-mediated relaxant responses and messenger RNA (mRNA) and protein expression of oestrogen receptor subtypes in the rat isolated bladder. Female Wistar rats (8 weeks) were anaesthetised, and the ovaries were removed (ovx) or left intact (sham). Rats were fed either normal rat chow (soy, phytoestrogens) or a non-soy (phytoestrogen free) diet. Isolated bladder from rats aged 12, 24 or 52 weeks were pre-contracted with 3 占carbachol prior to obtaining a concentration response curve to 17-߭estradiol. Protein and mRNA expression of the oestrogen receptor subtypes was completed using immunohistochemistry and real-time PCR, respectively. Relatively moderate relaxant responses to 17-߭estradiol were observed in bladders from all age and treatment groups. However, in soy-fed sham 52-week-old rats, the bladder exhibited enhanced relaxant responses to 17-߭estradiol when compared to tissues from other age-matched rat treatment groups (P??0.05). Diet, overiectomy or age did not alter the protein expression of either oestrogen receptor subtype in the bladder (P?>?0.05). While a soy diet improved relaxant effects to the 17-߭estradiol with age, it did not alter relaxant responses in bladders from ovariectomised rats.