Glomerular filtration rates (GFR) were determined with the use of iohexol clearance testing for 17 clinically healthy, captive, juvenile Kemp's ridley turtles (Lepidochelys kempii) and three Kemp's ridley turtles with histopathologically confirmed renal disease. Iohexol was administered intravenously at 75 mg/kg, and blood was collected 4, 8, and 24 h after injection. Plasma iohexol concentrations were determined by high-performance liquid chromatography, and GFR was calculated. Iohexol clearance rates for healthy turtles were 9–17.4 ml/kg/h (mean: 12.6, median: 13.2, standard deviation: 2.17), and those for renal disease turtles were 10.2, 3.0, and 9.2 ml/kg/h, respectively. Administration of intravenous iohexol to Kemp's ridley turtles appeared to be safe, as no adverse effects were detected. This study provides the first data for iohexol clearance in a chelonian species, and the first GFR data for Kemp's ridley turtles. Although the data are limited, this study suggests that iohexol clearance may be a useful noninvasive diagnostic tool for assessment of renal function in turtles.