The early (dynamic) and late (static) renal images obtained with 99m Tc-dimercaptosuccinic acid (DMSA) were utlized to evaluate renal cortical malignant tumors in 30 cases of renal cell carcinoma each of which had been confirmed by operation or autopsy. Early images, performed 20–50 seconds after radionuclide administration, demonstrated abnormal vascular pools in the cortex. A cold area without DMSA uptake was demonstrated on the 2-hour or late images, reflecting a non-functioning renal mass. Lesions demonstrated with combined early and late images showed a good correlation with those demonstrated by renal angiography in 25 out of 27 cases. However, when almost all the renal tumor was replaced by necrotic lesions, the early image did not reveal hypervascularity. When a highly vascular renal tumor extended to the perinephric tissues, the tumor area was sometimes overestimated on the early image. It is almost impossible to diagnose renal cell carcinoma using radionuclide imaging alone. However, 99m Tc-DMSA renal studies, using both early and late imaging, have proven to be a useful, noninvasive adjunct in the detection of malignant cortical lesions.