Reproducible and accurate myocardial T2* measurements are required for the quantification of iron in heart tissue in transfused thalassemia. The aim of this study was to determine the best method to measure the myocardial T2* from multi-gradient-echo data acquired both with and without black-blood preparation. Sixteen thalassemia patients from six centers were scanned twice locally, within 1 week, using an optimized bright-blood T2* sequence and then subsequently scanned at the standardization center in London within 4 weeks, using a T2* sequence both with and without black-blood preparation. Different curve-fitting models (monoexponential, truncation, and offset) were applied to the data and the results were compared by means of reproducibility. T2* measurements obtained using the bright- and black-blood techniques. The black-blood data were well fitted by the monoexponential model, which suggests that a more accurate measure of T2* can be obtained by removing the main source of errors in the bright-blood data. For bright-blood data, the offset model appeared to underestimate T2* values substantially and was less reproducible. The truncation model gave rise to more reproducible T2* measurements, which were also closer to the values obtained from the black-blood data.