This monograph, one of the Medical Extension Series prepared by the University of California at Los Angeles, is a collection of essays largely by members of the medical staff of U.C.L.A. on various agents causing diarrhea and their recognition. There are chapters on parasitic fungal, rickettsial, bacterial and viral diseases, on neoplastic and toxic diarrheas, on psychogenic diarrhea, on non-specific inflammatory disease, on non-abdominal occult diarrheas, on malabsorption syndromes in adults and in children, and on the special problems of diagnosis in infants and children.