This study was aimed; firstly to observe various clinical symptomatology with reiation to the number of Ancylostoma duodenale larvae orally given to the human beings, secondly to evaluate the effects of some drugs like steroid hormones, antihistaminic3 and antitussives, and, thirdly to study the influences of some iron compounds in prevention and treatment of anemia of such origin. Ten healthy volunteers free from the previous history of hookworm infection were divided into 4 groups, to whom various numbers of actively moving filariform Ancylostoma duodenale larvae were orally given; 500 to 4 cases, 250 to 3 cases and 100 to 3 cases. Following were the results: 1. Clinical symptomatology 1. The most frequently encountered symptoms and signs were general malaise, cough and hoar seness. The tracheal itching and pain low back pain, arthralgia, sputum and salivation, acid belching, loss of appetite, abdominal pain and vomiting were also noted. 2. If the larger number of the larvae was given, the clinical symtomatology was more severe. 3. Prednisolone medication caused some improvement of such symptomatology, while the antihistaminics and antitussives like codeine or ephedrine were ineffective. 4. In volunteers whose nutritional conditions were rather poor appeared to show more severe symptomatology. 2. Effects of iron compounds 1. The oral administration of ferrous fumarate induced a slight increase of serum iron levels in the initial stage of the infection, then a decrease from $15{sim}20$ days later and a recovery after 2 months. 2. The intravenous administration of saccharated ferric oxide induced a steady upkeep of the serum iron levels. 3. The hemoglobin contents also showed the upkeeps after either the oral or intravenous administration of the iron compounds. 4. The iron compounds, therefore, are considered to have the preventive as well as the therapeutic effects on hookworm anemia, which may strongly suggest that hookworm anemia is essentially the iron deficiency type. 3. Hematological changes 1. The severity of hookworm anemia generally correlated with the number of larvae given. 2. The moderate leucocytosis was observed in all cases regardless of the number of larvae given, which reached to a peak in $25{sim}35$ days. 3. Eosinophilia was observed in all cases, but was more severe in cases given larger number of larvae, which was slightly less evident after the medication of prednisolone. 4. Red cell survival time The red cell survival time determined by $^{51}Cr$ was generally in the normal ranges except for the severe anemia patients.