We studied 25 selected cases of anchylostomiasis, endeavouring to determine the factors which induce the hematic regeneration and investigating the mechanism of this regeneration as well as the development of the anemiant process. We preferred to select a small number of cases and accompany them for a long period, some of them having been underobservation during 1 to 1 year and a half. Apart from 568 routine examinations (count of red cells, dosage of Hb., determination of the hematokrit and, in the majority of cases, determination of the rate of reticulocytes, verifications of the morphologic aspect of blood on slides), the haematologic part consisted in investigations on globular resistence, rate of proteins in serum and, in some cases, count of platelets, determination of viscosity, etc. In these investigations we employed the usual methods, with the exception as for the determination of globular resistance, for which we described in detail a process though little used. During the whole course of the observations, the biologic activity of the helminthic parasites was controlled by numerous examinations of the faeces, consisting in the investigation of eliminated eggs and of chemical reactions detecting the presence of blood. Uranalyses were made periodically, and other examinations were practised whenever a complication or any unexpected fact came upon. In severe cases of the disease we observed an anemia of constant features. It is a hypochromic, microcytic and slightly regenerative anemia. We verified that the degeneration of the hematic indices, i. e. the degree of hypochromia and microcytosis in these extreme cases, does not appear in a variable but in a particularly constant manner; furthermore, we verified that these indices thus degenerated (Vol. Ind. 53 uc., Hb. Ind. 13'yy, Sat. Ind. 23%), according to observation by other authors, are also met with in various hypochromic anemiae of man or other mammals. Normoblasts, red cells with nuclear remainders and polychromatic red cells are extremely rare or even absent in the slides examined. This aspect is constant in severe cases; however, the number of these red cells characterized above is variable in the volume unit. The average of this reading is in numerous cases 2.50 M. which determines the rate of Hb, equal to 23%. After analysing certain observations which describe hematologic aspects different from those here described, we concluded that in such anomalous cases there are superpositions of other diseases, the etio-pathogenesis of which has nothing to do with the factors that determine the appearance of the anchylostomotic anemia. Hematic regeneration takes place in anchylostomiasis only after the administration of iron in variable doses, in conformity the salt employed. In the case here observed, the following prescriptions appeared inactive: raw liver, tryptophan, histidine, lecithin, Vit. B, arsenic, manganese, cobalt, copper and diets rich in iron. Owing to the results obtained by us through the separate administration of iron, we concluded that pyrrholic substances, liver fraction used in hypochromic anemiae and the association of iron with hydrochloric acid are inefficient. All these substances as well as the mere explusion of helminthic parasites, when used separately, not only appeared to have no action on the blood, but even did not help the regeneration induced by iron...