Radiation necrosis is the most common side-effect of stereotactic radiosurgery (SRS) and has similar characteristics to tumor progression on standard anatomical MRI. Differentiating these two conditions is a major long standing clinical challenge. In this study the potential of chemical exchange saturation transfer (CEST) in differentiating the two conditions in patient with brain metastases is investigated. The results showed that the magnetization transfer ratio (MTR) of amide and NOE peaks provided the best separation of radiation necrosis cases from tumor progression cases. However, the commonly used amide proton transfer (APT) was unable to differentiate the two conditions.