A collection of readily reproducible experimental methods for detecting free radicals and reactive oxygen species or their byproducts. The techniques range from established routine protocols to advanced methodologies using HPLC, mass spectrometry, and electron paramagnetic resonance. The HPLC techniques are applied to the electrochemical measurement of protein oxidation products, particularly nitrotyrosine and dityrosine, to the electrochemical detection of DNA oxidation products. There are also mass spectrometry methods measuring lipid oxidation products.