Traditional measurements of glomerular filtration rate (GFR) in clinical practice include the measurement of serum creatinine or creatinine clearance. Increasing evidence concerning the limitation of these measurements in clinical practice and clinical trials has resulted in efforts to develop technologies that improve measurement of GFR. Recent efforts in that regard have used radioisotopic labeling of markers of GFR, such as 125I-iothalamate, and 51Cr-ethylenediaminetetraacetic acid. Limitations of these technologies include radiation exposure as well as cost considerations for the management of radioisotopes, including safety, disposal, mailing, and deteriorating activity that results in short shelf life. We report a test that used 0.5 mL Conray dye injected subcutaneously and subsequent measurement of the nonisotopic (cold) iothalamate by capillary electrophoresis in blood and urine. GFR using cold iothalamate compared with standard clearance using 125I-iothalamate was 0.99. The method is cost-effective and allows for avoiding exposure to isotopes, as well as problems such as the disposal and short shelf life of isotopes. This technology could allow for replacement of 125I-iothalamate as a marker for GFR.