The authors quantified the collagen and elastic fibers in the bladder wall of ovariectomized rats with and without estradiol replacement. This study was conducted on 60 3-month-old Wistar rats. Group 1 remained intact; group 2 underwent bilateral ovariectomy and were sacrificed after 30 days; group 3 were sham operated and sacrificed after 30 days; group 4 had a bilateral ovariectomy and after 30 days were started on subcutaneous injections of 17beta-estradiol (10 mug/kg body weight) for 90 days; group 5 were sham operated and after 30 days were on started subcutaneous sesame oil replacement (0.2 ml/day) for 90 days; group 6 had a bilateral ovariectomy and after 30 days were started on subcutaneous sesame oil replacement (0.2 ml/day) for 90 days. Sirius red and Weigert's resorcin-fuchsin were used to stain collagen and elastic fibers on paraffin-embedded rat bladder sections. The M-42 grid system was used to quantitatively analyze the fibers. Ovariectomy had no effect on the volumetric density and absolute volume of the collagen and elastic fibers in the bladder wall of rats, or on the weight of the bladder. Estradiol replacement in castrated animals did not demonstrate any significant difference in the stereological parameters compared to the castrated group without hormonal replacement.142108112