Parasitic helminths exhibit greater diversity in energy metabolism than do the host animals and many have exploited unique respiratory chains as adaptations to their natural habitats. Cytochromes are involved, not only in intracellular aerobic respiration found in free-living stages, but also in the reduction of relatively oxidized compounds such as fumarate during the adult stages of parasitic helminths. In addition, most helminths retain a significant capacity to produce energy via aerobic pathways and have a mammalian type respiratory chain in their mitochondria during their development in the host. In this review, we focus on recent advances in the study of cytochromes in the respiratory chain of parasitic helminths. These include the identification of unique features of anaerobic respiration in adult parasites, the elucidation of molecular structures of the components involved and an understanding of the developmental changes that occur during the life-cycle of these parasites.