Because of the apparently increasing interest in the United States in the flagellates, and in compliance with numerous requests, a brief summary of the problem has been prepared from my Philippine records. No attempt is made to consider the biology of the parasites, because that is well done in a number of publications on parasitology. LAMBLIASIS,1 OR GIARDIASIS The synonyms of the term lambliasis, or giardiasis, are flagellate diarrhea (in part), tropical diarrhea (in part) and monad diarrhea (in part). It may be defined as an infection or infestation, principally of the intestine, byLamblia intestinalis(R. Blanchard, 1888), characterized by chronic diarrhea with intermittent acute exacerbations, digestive disturbances and nervous symptoms, or by the presence of the parasites without symptoms.Lamblia intestinalisis one of the common parasites, and lambliasis one of the common diseases, of the tropics. The intestinal or usual form of the disease is noted