Parasitic helminths which invade the body cavities and tissues of man and animals have developed specialized biochemical adaptations appropriate to this lifestyle. The study of their comparative biochemistry is concerned with determining the ways in which host and parasite metabolisms differ. The application of this information is vital in devising strategies for controlling parastic infestation. This text is an assessment of current ideas in the field, written by acknowledged world authorities. Wide-ranging in approach, its coverage includes: specialized biochemical adaptations and their significance; the function of monamines in metabolism and neurobiology; the evolutionary significance of oxygen and parasitic adaptation, detoxification reactions and drug inactivation functions; and the role of molecular biology in drug resistance. Examples of the application of modern techniques, such as nuclear magnetic resonance spectroscopy, to the study of parasite metabolism are cited but with the emphasis on topics of current concern rather than specialized data.