We investigated the effect of thiamine (131) treatment on bladder dysfunction in streptozotocin (STZ)-induced diabetic rats. A total of 40 rats were randomly divided into four groups: a control group, a group given thiamine only, a diabetic group and a diabetic group given thiamine therapy. Diabetes was induced in the rats by 65 mg/kg STZ via an intraperitoneal injection. Thiamine was given 50 mg/kg/day. Diabetic cystopathy was confirmed on cystometry 8 weeks later in diabetic groups. Rats' body and bladder weights were measured. Contractile response to carbachol and potassium chloride (KCl) of detrusor strips in all groups was studied in vitro. The body weights were significantly decreased (p < 0.01), the bladder weights were significantly increased (p < 0.01), and the cystometric bladder capacity and the residual urine volumes were significantly increased (p < 0.001, p < 0.01 respectively) in STZ-induced diabetic groups compared to the control group and the group given thiamine only. Contractile responses increased in the diabetic group in high carbachol and KCl concentrations (p < 0.01, p < 0.01, respectively). On the other hand, there were no differences in the other groups. These data suggest that high-dose thiamine (B1) treatment may be beneficial in delaying the progression of diabetic cystopathy in this experimental animal model.