Stimulated by the impressive effect of interferon beta on magnetic resonance imaging-detected disease activity, the past year or so has seen a particular interest in the use of magnetic resonance imaging to monitor treatment. To be effective in this regard, there needs to be a high sensitivity and accuracy in detecting disease activity, and the imaging findings should be predictive of clinical outcome, especially disability. A number of approaches show promise as being more sensitive than the conventional T2-weighted sequence. Furthermore, conventional magnetic resonance imaging cannot identify demyelination and axonal loss, the pathological substrates of irreversible disability. Newer magnetic resonance imaging techniques may be more pathologically specific, for example magnetization transfer imaging and magnetic resonance imaging spectroscopy. Such techniques provide new insights into the pathophysiology of multiple sclerosis. Improved methods for examining the often disabling spinal cord lesions have also emerged.