The study investigated the effect of a traditional Chinese herbal preparation 'Ba-Wei-Die-Huang-Wan' on the cholinergic function of the urinary bladder in diabetic rats, as well as its influence on the protein expression of muscarinic M(2) receptors. Wistar rats were divided into three groups: (1) control rats; (2) 2-week streptozotocin-induced diabetic rats; and (3) diabetic rats treated with Ba-Wei-Die-Huang-Wan 26 mg/kg thrice daily for 3 days. A dose-response study was performed for bladder muscle strip contractile response to a muscarinic agonist, arecaidine propargyl ester (APE). The amount of M(2) receptor protein in the bladder was measured by Western immunoblotting using monoclonal antibodies. The bladder contractile response to APE was significantly increased in the diabetic rats compared to the control. The M(2) receptor protein density was also significantly higher by 106% (P < 0.01, n = 8) in diabetes. Ba-Wei-Die-Huang-Wan treatment significantly lowered the plasma glucose level of the diabetic rats. The increases in contractile response to APE as well as the M(2) receptor protein density were partially reversed by the treatment. In conclusion, there was an over-expression of M(2) receptor resulting in hyper-contractility in the bladder of diabetic rats. Ba-Wei-Die-Huang-Wan significantly alleviated the alterations.