THE PARASITIC DISEASES of man which are found primarily in the small bowel are caused by both protozoa and helminths. In this region of the bowel, protozoa are not of major importance, but giardiasis may produce mild symptoms in infants, in whom the infection is more prevalent.Giardia lambliais found much less frequently in adults, but heavy infections may produce mild but chronic clinical manifestations. This organism is actually the only protozoan parasite found in the small intestine which is of any importance to the clinician. Quinacrine (Atabrine) hydrochloride is highly effective againstGiardia lamblia. It should be given by mouth after meals for 5 days. The individual dosage is 0.05 gr twice daily for children 1 to 4 yr of age; 0.1 gr twice daily for those 4 to 8; and 0.1 gr three times a day for persons over 8 yr. Only occasionally is a second course