X-ray fluorescence analysis provides a simple method of measuring glomerular filtration rate from the clearance unlabeled radiographic contrast media. To measure the accuracy iopromide clearance using a clinically simple 2-sample single injection technique, a comparison was made in 29 patients with 51Cr-EDTA clearance. The clearance of iopromide and 51Cr-EDTA were virtually identical (r = 0.967) and no side effects of the procedure were noted. Iopromide clearance using X-ray fluorescence is simple, rapid, safe and accurate method to determine glomerular filtration rate for research and clinical purposes.