The pharmacokinetics of tempo carboxylic acid (TCA), a nitroxyl contrast medium have been evaluated in control and streptozocin-diabetic rats. Previous magnetic resonance imaging (MRI) studies in diabetic rats showed prolongation of contrast visualization in the renal cavities after injection of TCA. Diabetes induced only slight alterations to the pharmacokinetic parameters. Rate constants and half lives were unchanged after four months of diabetes. A significant decrease of the apparent total body clearance and volume of distribution was observed while the area under the curve was increased. These alterations are not sufficient to explain MRI abnormalities which have to be elucidated.