New techniques of functional brain mapping using magnetic resonance imaging (fMRI) are described. Methods monitoring blood oxygenation and blood flow changes are distinguished and compared. The major sources of artifact, subject motion and contamination of the functional image by large veins, are discussed, and methods of data analysis are reviewed. A survey of the numerous preliminary fMRI studies in cognitive neuroscience is presented, with specific attention to recent studies of language areas in deaf subjects and the cortical effects of motor training.