Wool fibers were chemically modified by reaction with succinic and glutaric anhydrides. The weight gain land acyl contest) increased with increasing the reaction temperature (65-80 degrees C) and time (1-2 h), attaining 18.9% (158.9 mol/10(5) g) and 23% (163.9 mol/10(5) g) for succinylated and glutarylated wool, respectively. Changes in the amino acidic pattern of acylated wool, i.e., decrease of basic amino acid residues and formation of ornithine, were observed by acid hydrolysis. The X-ray diffraction profiles of modified wool fibers remained essentially unchanged, suggesting that the crystalline structure was not affected by reaction with acid anhydrides. The degree of molecular orientation of acylated wool slightly decreased, especially at high weight gain. The viscoelastic response of wool modified with succinic and glutaric anhydrides was characterized by a shift, to a lower temperature of both the drop of the storage modulus and the peak of the loss modulus, These features are indicative of a higher mobility of the keratin chians in the amorphous and crystalline domains. In fact, it is suggested that the chemical agent diffused into the accessible parts of cu-crystallites, reaching the available reactive sites. This did not cause changes in the crystalline pattern of wool, but resulted in a different thermal behavior of fibers.