Detrusor overactivity(DO)persists after prostatectomy in 20% to 25% of patients with benign disease.Assuming that nonvoiding contractions(NVCs)can be used as a surrogate for DO in humans,the rat model of obstruction/deobstruction may allow us to study the pathophysiology of persistent DO after deobstruction.We investigated bladder function,with a special focus on NVCs,in rats by use of a new,modified method of obstruction and deobstruction and compared these results with those obtained by use of the conventional method.Seventy female Sprague Dawley rats underwent 1)sham operation(n=10),2)obstruction by a modified method(Modif-Obs; n=12),3)obstruction/deobstruction by the conventional method(Conv-Obs/Deobs; n=1 3),or 4)obstruction/deobstruction by the modified method(Modif-Obs/Deobs; n=35).The Modif-Obs/Deobs animals were divided into subgroups with(DO+)and without(DO-)NVCs.Two weeks after partial urethral obstruction,the animals were deobstructed,and 1 week later cystometry was performed with recording of intra-vesical and intra-abdominal pressures.NVCs were shown in all groups:Modif-Obs(80%),Conv-Obs/Deobs(100%),and Modif-Obs/Deobs(40%).In the Modif-Obs/Deobs group,bladder weight and the muscle/collagen ratio were higher in DO+ than in DO-rats.The Modif-Obs/Deobs group showed no mortality compared with 25% mortality in the Conv-Obs/Deobs group.The modified method may be more adequate for studying persistent DO after deobstruction,because it resulted in pressure/volume-and DO-related parameters similar to those found in the clinical situation.The persistence of DO after deobstruction may partly be due to irreversible changes in the bladder caused during the period of obstruction.