The transverse relaxation time of water protons is shortened by the presence of iron. This shortening depends on the amount and the environment of iron in the sample. We have developed a method for measuring short transverse relaxation time noninvasively by magnetic resonance spectroscopy. To evaluate magnetic resonance spectroscopy as a means of assessing hepatic iron content in patients with transfusional iron overload, we compared the results obtained with this method with those obtained by other means of assessing total body iron content. The correlation between the liver biopsy iron concentration and l/transverse relaxation time was highly significant (r = 0.96, p < 0.004, n = 6) for iron loads up to 3% dry weight. The correlation between serum ferritin and Utransverse relaxation time was also significant, but the correlation coefficient was much lower (r = 0.67, p < 0.002, n = 20). The correlation between 24-hr urinary iron excretion and l/transverse relaxation time was not significant, nor was that between AST and l/transverse relaxation time. We conclude that magnetic resonance spectroscopic determination of the transverse relaxation time of hepatic water is an accurate method of measuring liver iron content, especially when the iron content is below 3%. Because it is a noninvasive method that is associated with negligible side effects, it could provide clinicians with an excellent means of assessing the effectiveness of the various therapeutic strategies used in the management of patients with iron overload. (HEPATOLOGY 1994;19: 904-910.) The long-term transfusion therapy that is essential for normal life in p-thalassemia major (1-3) causes iron deposition in organs such as the heart (41, liver (5) and endocrine glands (6). If untreated, iron overload causes widespread organ damage and leads to early death of cardiac toxicity or liver failure (7). Patients with thalassemia are therefore treated by chelation therapy, usually