Neurological disorders (NDs) such as Alzheimer’s disease, Parkinson’s disease and multiple sclerosis all come with increased oxidative stress, linked to the production of reactive oxygen species (ROS). Under healthy conditions, various antioxidant molecules containing sulfur or selenium are involved in avoiding redox homeostasis imbalance. As a result of physiological changes occurring in the brain of patients suffering from one of the NDs mentioned above, changes in the isotopic composition of S and Se are expected, due to changes in the isotope fractionation accompanying biophysical and biochemical processes. We will use multi-collector ICP-mass spectrometry to reveal and quantify such changes in S and Se isotope ratios in the biofluids cerebrospinal fluid CSF and serum (patients and murine models) and in several brain regions (murine models). We aim at a deeper insight into the local S and Se biochemistry and an evaluation of high-precision isotopic analysis of S and/or Se as diagnostic/prognostic tool in this context.