The aim of this study is to determine the early effects of partial outflow obstruction (POO) on the detrusor contractility of diabetic (DM) and non-diabetic rats. A total of 67 adult female Wistar rats with average weight of 214+/-3.1 g were randomized into five groups as control ( n=6), sham operated ( n=6), obstructed ( n=18), DM ( n=19), and DM with obstruction ( n=18). Intraperitoneal injection of 60 mg/kg streptozotocin was performed to achieve DM. Partial bladder neck obstruction was created surgically by ligating the urethra around a 3F feeding tube. Bladder strips were obtained and inspected on days 3, 7, and 14 of both the diabetic period and POO. Mean detrusor weights were measured and the maximal contractile responses to carbachol (Car), adenosine 5'-triphosphate (ATP), substance P (SP) and electrical field stimulation (EFS) of detrusor strips in all groups were studied in vitro. After 14 days of obstruction, no remarkable difference was observed between the maximal contractile responses to Car and SP of strips from obstructed-only (POO) and diabetic-obstructed (DM-POO) rats compared to the control group. The responses to EFS and ATP in the POO rats were significantly lower than the controls ( P<0.01, P<0.01, respectively). In the DM-POO group however, the responses were significantly better than the POO group, reaching almost similar levels with the controls. The contractile responses of DM-POO rats were higher than the POO group but lower than the DM group. Better contractile responses of the rats with DM-POO than POO group can be explained by the early enhancing effects of DM on detrusor contractility. In early DM+POO period, the negative effects of POO on detrusor muscle contractility is masked by diabetes mellitus.