1.1. The endoparasite Strongyluris brevicaudata, found in the rectum of the African lizard Agama agama, contained 9.3–11.7% glycogen.2.2. The ratio of carbon dioxide liberated to oxygen consumed by live parasites in vitro was found to be about 0.78.3.3. The steady-state contents of lactate and succinate in freeze-clamped parasite tissues were higher than those of other metabolites involved in anaerobic energy metabolism.4.4. Extracts of parasite tissues contained high levels of malate dehydrogenase (MDH), NAD-specific malic enzyme (ME) and phosphoenol pyruvate carboxykinase (PEPCK) and a low level of pyruvate kinease (PK). The PK/PEPCK ratio was 0.19.5.5. MDH, PK and PEPCK activities were found in the cytosol fraction whereas ME, fumarase and fumarate reductase activities were found mainly in the mitochondrial fraction.6.6. Fumarate reductase activity was enhanced about 4-fold in the presence of ADP and Pi (2.0 mM).