Scintigraphy with Tc-99m MAG3 is, to date, the most commonly used technique for evaluating separate renal function (SRF). In this study, the performance of this technique is compared to Tc-99m DMSA. A total of 37 patients with various kidney disorders (12 children and 25 adults) underwent both Tc-99m DMSA and Tc-99m MAG 3 sclntigraphy. In children and adults of normal weight the correlation coefficient between the two methods was 0.99 (P< 0.001), whereas in individuals who were more than 10% overweight according to Broca, or who had abnormal anatomical positions of the kidneys, the correlation coefficient was 0.82 (P< 0.05). Sclntigraphy with Tc-99m DMSA was more accurate in renal parenchyma lesions. These results indicate that Tc-99m DMSA sclntigraphy is preferable for the evaluation of SRF in patients who are more than 10% overweight, or have abnormal positions of the kidneys.