In vivo nuclear magnetic resonance (NMR) spectroscopy is a rapidly developing, noninvasive analytical technique that allows sequential studies of brain tumor metabolism. It can be implemented on most conventional high-field magnetic resonance imaging scanners. In animal tumor models, NMR spectroscopy has been used extensively to characterize the metabolic changes associated with tumor growth and response to therapy. Preliminary data in humans indicate the feasibility of recording phosphorus and proton spectra from focal lesions within the brain. It is hoped that the technique will provide useful prognostic information in terms of tumor growth behavior and prediction and detection of response to therapy. However, the technique suffers from relatively coarse spatial resolution, and the methodology is still under development. More studies with larger patient groups are required before the clinical utility of the technique can be fully evaluated.