Ten normal volunteers and 45 patients with breast abnormalities were examined with magnetic resonance (MR), utilizing a 0.3-tesla superconducting magnet. In all patients, MR detected an abnormality that corresponded to the area of pathology seen on either a mammogram or computed tomographic (CT) scan. An appreciable advantage of MR over mammography was observed in patients with cysts and in those with areas of asymmetric dysplastic breast tissue. Abnormalities on MR images appeared as areas of low signal intensity relative to adjacent normal ductal and fatty tissue. The configuration of a lesion on MR permitted distinction between a benign and a malignant process.