Magnetic resonance imaging (MRI) at 0.35 T with a superconductive magnet was performed on 80 patients with known or suspected malignant disease of the bone marrow. The group comprised 50 patients with known primary malignancy and 30 with known multiple myeloma. The MRI scan was correlated with plain films and radionuclide bone scans. In 40 patients with suspected metastatic disease, areas of decreased signal intensity on T1-weighted spin-echo images were observed. Ten patients had no MRI evidence of metastasis, and the abnormalities suspected on bone scanning were shown to be due to other causes. All the myeloma patients had abnormalities demonstrated by MRI. This was significant, since most had normal bone scans. All diagnoses were confirmed by needle biopsy. MRI was shown to be a sensitive method of detecting areas of malignancy within the bone marrow toward which biopsy could be directed.