Magnetic resonance imaging (MRI) of the breast was performed in 35 women using a prototype breast coil at 0.15 T. The distribution of fibroglandular and fatty tissues was demonstrated sufficiently well to permit correlation with the mammographic patterns of Wolfe, and it was possible to identify 1-cm cysts. The signal intensity of the cysts varied from low to high as repetition time (TR) and echo time (TE) using the spin echo technique (TR/TE) were prolonged from 250/30 to 1,000/120. In two women, fibroadenomas were seen as low-intensity, smoothly marginated lesions surrounded by fat. A range of in vivo observed T1 values is summarized for normal and pathologic tissues. It is concluded that MRI of the female breast, currently in the developmental phase, is feasible and further evaluation is indicated.