Acid hydrolyzates of waxy-maize starch were separated to give Fractions I, II, and III [T. W atanabe, and D. F rench, Carbohydr. Res., 84 (1980) 115–123]. Watanabe and French suggested that Fraction II, which contains approximately 25 d-glucose residues including an α- d-(1→6)-linked branch, has a double helical structure. In the present study, the thermodynamics of binding of iodine to Fractions II and III, and debranched Fraction II (Fraction II′) was measured by isothermal-flow calorimetry. If four binding sites for Fraction II and two for Fractions II′ and III are assumed, the standard free-energy changes, Δ 0 b, for the binding of I 2 are −18.5, −18.8, and −18.4 kJ·(mol I 2) −1, and the enthalpy changes, Δ H b, are −28.4, −24.7, and −26.9 kJ·(mol I 2) −1, respectively. The similarity of these values for the three fractions indicates that the conformation of Fraction II is essentially the same as those of Fractions II′ and III, and that Fraction II, therefore, does not have a double helical structure in solution. The values for Δ G 0 b are ∼15 kJ·mol −1 less negative, and those for Δ H b ∼40 kJ·mol −1 less negative than published values for the starch-I 2 complex. These differences are due to the relatively very short d-glucose chains in the amylodextrin fractions employed in the present work.