The major soil-transmitted intestinal nematodes of humans, Trichuris, Ascaris, and the two major hookworms, Ancylostoma and Necator, often are referred to collectively as geohelminths. Geohelminth infections are a particular public health threat to children in whom high intensity infections frequently occur. For Ascaris and Trichuris, the heaviest and most severe infections occur in children of school-age. As a result, these children suffer unique geohelminth-associated deficits in physical and intellectual growth. In a few cases, the parasite-derived macromolecules partly associated with these processes have been identified and chemically characterized. Copyright © 2000 by W.B. Saunders Company