The modulation of urinary bladder function by sex hormones was examined in castrated and sham-operated male and female streptozotocin-diabetic rats. Male and female diabetic rats weighed less than age-matched controls and had significantly greater serum glucose levels and bladder weights. Castration had no effect on bladder mass and did not alter the diabetes-induced changes in rat or bladder mass. Protein concentrations were significantly increased and collagen concentrations were significantly decreased in bladders from diabetic rats compared with non-diabetics. Sex or castration had no effects on protein or collagen concentration of bladders from nondiabetic and diabetic rats. There were no differences in water consumption and urine excretion between male and female nondiabetic rats, and no effects of castration were observed on micturition in nondiabetic rats. Ovariectomy followed by diabetes caused a significant increase in urine excretion compared with diabetes alone. Ovariectomized diabetic rats had increased mean and maximal micturition volumes when compared with other female rats. Orchiectomy had no effects on the expected increases in micturition associated with diabetes. Diabetes in male rats caused significant increases in contractile responses of bladder strips to field stimulation, carbachol, KCl and high concentrations of ATP. In both nondiabetic and diabetic groups, orchiectomy had no effects on the contractile responses compared with sham operation. Similarly, in bladder strips from diabetic females, contractile responses to carbachol, KCl and high concentrations of ATP were significantly increased compared with those of nondiabetics, and were unchanged by ovariectomy. However, ovariectomy in nondiabetic rats caused significant decreases in contractile responsiveness to nerve stimulation, effects which were only partially prevented by diabetes. The data suggest that there are few differences between male and female rats in their sensitivity to streptozotocin and the effects of diabetes on micturition, bladder collagen and protein concentration, and the responsiveness of bladder strips to contractile agents. The changes in bladder function observed after induction of diabetes do not appear to be related to changes in sex hormone levels. The major differences noted between males and females were the decreased responsiveness of bladders from nondiabetic ovariectomized female rats to field stimulation. In conjunction with previous data obtained in this laboratory, the study suggests that the responses to field stimulation are more sensitive to the effects of ovariectomy than are the responses to contractile agonists.