Intravenous contrast media are widely used in MR imaging of the brain. Clinical utility is high in both neoplastic and non-neoplastic disease. The agents approved to date are all gadolinium chelates, with extracellular distribution and renal excretion. The agents differ in regard to the maximum dose that can be administered and the theoretical safety margin. When administered at the same dose, the efficacy of the different available agents is comparable. Described in the following review article are the diagnostic use of contrast media and the patterns of enhancement encountered in neoplastic disease, infection, vascular disorders, and diseases of white matter. Only in congenital brain disease, when acute abnormalities are not suspected clinically and neoplastic disease is not a question, is contrast enhancement not indicated. The gadolinium chelates play a major role in the evaluation of patients by MR with known or suspected brain disease. These agents improve both the sensitivity and specificity of the examination. In many cases, lesions cannot be identified before contrast administration. Lesion delineation, assessment of lesion activity, and differential diagnosis are all improved, in general, with the addition of postcontrast scans. The scope of applications continues to expand as the modality and clinical experience matures.