Bruker BioSpin Corporation 1 article published in JoVE Biochemistry Use of Electron Paramagnetic Resonance in Biological Samples at Ambient Temperature and 77 K Hanan B. Elajaili1, Laura Hernandez-Lagunas1, Kalina Ranguelova2, Sergey Dikalov3, Eva Nozik-Grayck1 1Cardiovascular Pulmonary Research Laboratories and Pediatric Critical Care Medicine, Department of Pediatrics, University of Colorado Anschutz Medical Campus, 2Bruker BioSpin Corp, 3Department of Medicine, Division of Clinical Pharmacology, Vanderbilt University Medical Center Electron paramagnetic resonance (EPR) spectroscopy is an unambiguous method to measure free radicals. The use of selective spin probes allows for detection of free radicals in different cellular compartments. We present a practical, efficient method to collect biological samples that facilitate treating, storing, and transferring samples for EPR measurements.