The advantages of synchrotron radiation have been employed to revitalize a 60-year-old technique for measuring anomalous scattering factors by accurately measuring x-ray refraction through a prism. We report results obtained from a GaAs sample in the vicinity of both the Ga and As K absorption edges. Our analysis of the technique shows that relative accuracies of 0.03 electrons and absolute accuracies of 0.1 electrons should be readily obtainable. This should be adequate for the needs of anomalous x-ray scattering measurements.