Magnetic resonance imaging (MRI) of the breast was performed in 10 volunteers and 102 women with suspected breast disease, using a 0.35-T superconducting magnet. All patients had prior x-ray mammography. MRI was superior to mammography in differentiating solid from cystic lesions and equivalent to mammography in providing information regarding different parenchymal patterns. Of 21 surgically proven carcinomas of the breast, MRI correctly identified 18 and mammography identified 19. The major disadvantage of MRI is its inability to show calcifications, benign or malignant. Future studies will be needed to show the relative values of sonography and MRI in detecting small cysts. In addition, MRI in future should be able to demonstrate small, noncalcified masses in mammographically dense, fibrocystic breasts.