Reactive oxygen species (ROS) represent a number of highly reactive oxygen-derived by-products generated by the normal mitochondrial respiration and other cellular metabolic reactions. ROS can oxidize macromolecules including lipids, proteins, and nucleic acids. Under physiological condition, the cellular levels of ROS are controlled by several antioxidant enzymes. However, an imbalance between ROS production and detoxification results in oxidative stress, which leads to the accumulation of macromolecular damage and progressive decline in normal physiological functions. Oxidative deterioration of DNA can result in lesion that are mutagenic and contribute to aging and age-related diseases. Therefore, methods for the detection of ROS and oxidative deterioration of macromolecules such as DNA in cells provide important tool in aging research. Here, we described protocols for the detection of cytoplasmic and mitochondria pools of hydrogen peroxide, and the DNA modification 8-oxoguanine, a biomarker of oxidative damage, that are applicable to cell-based studies on aging and other related areas.