Intestinal parasites not only cause diarrheal illnesses but may also cause significant malabsorption in man. Separation of true malabsorption caused by a particular parasite from other factors that may coexist with and even mimic malabsorption, such as malnutrition may be very difficult. Despite these problems, it appears that giardiasis, coccidiasis, strongyloidiasis and capillariasis cause malabsorption of many important nutrients. D. latum interfere with vitamin B12 absorption.