Mitochondria are essential organelles with central roles in diverse cellular processes such as apoptosis, energy production via oxidative phosphorylation, ion homeostasis, and the synthesis of heme, lipid, amino acids, and iron-sulfur clusters. Defects in the mitochondrial respiratory chain lead to or are associated with a wide variety of diseases in humans. The nematode Caenorhabditis elegans provides a powerful genetic and developmental model system for reproducing deleterious mutations causing mitochondrial dysfunction and investigating their metabolic consequences and their mechanisms of pathology. In this chapter, we describe the growth of C. elegans in liquid culture, the isolation of crude and purified mitochondria, and polarographic and histochemical approaches for measuring mitochondrial respiratory chain function.