The feeding behavior of Ancylostoma caninum was studied to define its relationship to associated blood loss. Wells' method of observing worms in vivo was used, and the observations were extended to worms and tissues that were fixed together after various periods of 1 to 18 minutes and up to 2 hours. At necropsy attached worms were excised together with adjacent intestine and fixed in situ. Changes in the tissues surrounding and ingested by the worms were used in reconstructing the probable sequence of feeding and related events. Observations revealed that feeding is essentially restricted to the mucosa. When mucosa is sucked into the buccal capsule, detached epithelium is carried into the worm's intestine along with blood from ruptured vessels. The remaining indrawn tissue becomes constricted at the buccal orifice as the mass of lamina propria is drawn from the surrounding areas toward the opening, and the host tissue in the capsule of the worm is broken down and sucked into the midgut after which a new “bite” is taken. Hemorrhage at the site of attachment appears to be of considerable importance in the manifestations of hookworm disease.