The activity of pancreatic a-amylase is increased in the presence of Hymenolepis diminuta, although the intact worms show no intrinsic amylolytic activity. Enhancement of amylase activity is a function of the number of worms present. Maximum relative enhancement occurs at very low enzyme concentrations, and there is an apparent increase in maximum velocity when substrate concentration is varied. The effect is readily reversible and is inhibited by polycations. Killed worms produce no enhancement of amylase activity. It is concluded that a surface adsorption is involved and the possible structural relationships are briefly discussed. The importance of differentiating intrinsic from adsorbed enzymes is also discussed. Previous studies of the brush border of the mammalian small intestine have shown that there are intrinsic, membrane-bound disaccharidases and phosphohydrolases in the outer cell surface (Crane, 1962; Newey et al., 1963). Similarly, the tapeworm Hymenolepis diminuta has been shown to have surface phosphohydrolases (Arme and Read, 1970; Dike and Read, 1971a, b). Further, the tapeworm enzyme seems to be spatially adjacent to the membrane system involved in glucose transport: The glucose product of glucose-6-phosphate hydrolysis has a kinetic advantage for absorption rather than for diffusion into the surrounding medium in vitro (Dike and Read, 1971b). In addition to intrinsic digestive enzymes, adsorbed digestive enzymes have been reported to be associated with the mammalian brush border. These are pancreatic in origin and have been referred to as contact digestive enzymes (Ugolev, 1965; De Laey, 1966a). Such enzymes are thought to be bound to the brush border fuzzy coat by electrostatic charge (De Laey, 1966b). Binding seems to depend on surface area available (De Laey, 1966c, 1967) and is readily reversible (Jesuitova et al., 1964). The kinetic parameters of pancreatic amylase are reported to change with adsorption to the brush border. However, some doubt has been cast on the conclusion that adsorption of pancreatic amylase to the mucosal surface enhances the action of the enzyme. McMichael and Dahlqvist (1968) and Alpers and Solin (1970) have shown that Received for publication 14 September 1971. * This work was supported by a grant from the NIH, U. S. Public Health Service (AI 01384). there are membrane-bound intestinal amylases in man and the rat. These are intrinsic to the mucosal surface and differ from pancreatic amylase in a number of respects. It has been pointed out that failure to recognize the presence of these membrane-bound amylases could lead to an erroneous conclusion that there is an enhanced activity of pancreatic amylase in the presence of mucosal tissue. Taylor and Thomas (1968) reported that the presence of tapeworms (three species) increased the rate of starch hydrolysis by bacterial a-amlyase in vitro and that the degree to which the enzyme was affected was related to worm surface area. The present study is an examination of this phenomenon, using pancreatic a-amylase and the rat tapeworm Hymenolepis diminuta. MATERIALS AND METHODS Hymenolepis diminuta was reared in the beetle Tenebrio molitor. Young male rats of the Holtzmann strain (Sprague-Dawley derived), weighing 100 to 120 g, were infected with 30 cysticercoids of H. diminuta. Ten or 11 days after infecting a group of rats, they were killed and worms flushed from the gut with a Ringer saline containing 25 mr tris-maleate buffer at pH 7.2 (KRT of Read et al., 1963). Worms from a group of rats were randomly distributed into samples, usually 15 worms per sample. Amylose hydrolysis was measured colorimetrically at 690 nm, using the iodine reagent described by Taylor and Thomas (1968). At this wavelength, the color obeys Beer's law between 10 and 120 /ug of amylose. A typical curve with varying concentrations of a-amylase is shown in Figure 1. Amylase was also determined by the method of Ujihara et al. (1965). To detect substrate hydrolysis, 3,5-dinitrosalicylic acid was added just prior to stopping the reaction by boiling. The absorbance was read at 520 nm. Standard