In this study, we tried to elucidate the effect of estrogen treatment on the detrusor contractile response to muscarine and muscarine receptor subtypes of the bladder in 13-month-old female Wistar rats. The rats were divided into two groups, controls and rats treated with estradiol for 12 weeks. After the treatment phase, we monitored micturition behavior in addition to performing cystometrograms after the administration of muscarine, and real-time polymerase chain reaction for mRNA expression of the muscarinic receptor subtypes in the detrusor muscle. Our data indicated that there was a significant increase in the maximum micturition volume in the estradioltreated rats. The urodynamic results indicated significant changes in the maximum detrusor pressure following the administration of muscarine in the estradiol-treated rats, in contrast to the controls for which no significant changes were observed. Furthermore, M₃ receptor mRNAs in the detrusor muscle were significantly decreased in the estradiol-treated rats as compared to the control rats, while there were no differences noted for the M₂ receptor mRNAs. Our data demonstrates that long-term estradiol treatment might be capable of increasing the potential detrusor contractility, and thus, estradiol might be a therapeutic agent that can be used to target the M₃ receptors during the treatment of detrusor instability.