A pilot study was carried out in order to determine the possible applications of nuclear magnetic resonance (NMR) imaging in the diagnosis of renal disease. 22 patients with various benign and malignant tumors as well as renal parenchymal disease and chronic rejection in transplant kidneys were studied with a Philips resistive prototype scanner and the superconducting Gyroscan S5. Contrast resolution and therefore tissue differentiation are excellent. A hemorrhagic cyst can be differentiated from a simple cyst. Diffuse and patchy parenchymal changes are diagnosed in an objective and quantitative way. Lesions as small as 1 cm are easily detected and NMR is potentially more accurate than X-ray CT in the local staging of renal cell carcinoma. A disadvantage is the inability to detect calcifications. We conclude that NMR is a highly sensitive modality and appears to be more specific than X-ray CT and ultrasound.