Laboratory investigation in rats submitted to experimental spinal cord injury (SCI). To characterize changes in renal function during acute SCI. Sprague Dawley rats were subjected to severe spinal cord contusion at T8 level or to laminectomy as control. Twenty-four hours after spine surgery, clearance assessments of a single dose of iohexol (120 mg kg(-1)) or of p-aminohippuric acid (PAH, 100 mg kg(-1)) were used to evaluate glomerular filtration rate (GFR) and tubular secretion (TS), respectively. Blood sampling was used to determine concentrations of both compounds by high-performance liquid chromatography for pharmacokinetic measurements. Iohexol clearance decreased significantly after injury, which resulted in increased concentrations and half-life of iohexol in blood; PAH clearance remained unchanged. GFR but not TS is altered during spinal shock. These observations should be of interest to professionals caring for early cord-injured patients, in order to prevent toxicity and therapeutic failure when administering drugs eliminated by the kidney.