To investigate whether alpha1-adrenoceptors are involved in pain behaviors in streptozotocin (STZ)-induced diabetic rats, we measured the effects of phenylephrine or prazosin on allodynia in the diabetic rats. Phenylephrine aggravated allodynia, while prazosin alleviated allodynia in the diabetic rats. We also measured alpha1-adrenoceptors gene expression or density of [3H]-prazosin binding sites in the dorsal root ganglia (DRG) and spinal cord in painful diabetic rats. Alpha1-adrenoceptors mRNA and density of [3H]prazosin binding sites were increased in the DRG of the diabetic rats, however there were no significant differences in alpha1-adrenoceptors expression in the spinal cord between the control and diabetic rats. These results suggest increased alpha1-adrenoceptors in the DRG may play a role in the pathogenesis of painful diabetic neuropathy.