The dynamic activity of endosomes and peroxisomes is observable in the digital video sequences of U2OS cells presented in this section. The organelles were visualized with green fluorescent protein (fused to peroxisomal targeting signal) and mCherry (fused to endosomes). Endosomes and peroxisomes are both types of membrane-bound compartments found in eukaryotic cells, though they typically differ in the materials they hold and their functionality. Dozens of oxidative enzymes can be found inside peroxisomes, which play a critical role in cell detoxification and the metabolism of fatty acids and various metabolites. Endosomes, however, are part of the endocytic pathway that materials internalized from outside of the cell through endocytosis follow. In addition to foreign molecules, endosomes usually contain a variety of receptors, ligands, and molecules responsible for maintaining the internal environment of the compartment.