Brain edema is one of the most common morbidity factors in patients with intracranial neoplasms and cerebrovascular pathology. Monitoring of intracranial pressure gives only an indirect and global measure of brain swelling. We have made an assessment of the applicability of Raman spectroscopy as an alternative method for assessing brain edema, which measures the water concentration in the tissue directly. Partial least-squares models were developed on the basis of Raman spectra measured in the 2600-3800-cm(-1) region, which predict the water fraction of brain tissue in the 0.75-0.95 range, with an accuracy better than 0.01.