Heterogeneous populations of mitochondria have been described in helminths. Mitochondria from different tissues have been isolated in adult organisms. However, in larvae, due to their small size, isolation from tissues has not been feasible. A method for the isolation of tegumental mitochondria from the larval stage of Taenia crassiceps is described. After solubilization of the plasma membrane with saponin, tegumental mitochondria were purified by a simple and rapid protocol of differential centrifugation, which allowed the retention of suitable quantities of well-preserved mitochondria, as judged by biochemical and ultrastructural parameters. Respiratory activity evoked by exogenous NADH was negligible, but its oxidation increased several-fold after sonication of intact mitochondria. Other substrates, e.g., succinate and malate-glutamate, were oxidized at high rate, leading to the formation of a H+ gradient across the inner mitochondrial membrane, which, in turn, supported oxidative phosphorylation. These results indicate that tegumental mitochondria carry out aerobic metabolism.