Because of conflicting reports and unrealistic literature values, a systematic study of the surface energy of chitin, chitosan, and their respective monomeric counterparts was carried out using contact angle measurements on films and pellets, before and after different purification procedures. All the commercial samples of these polymers were shown to contain nonpolar impurities that gave rise to enormous errors in the determination of the polar component of their surface energy. After their thorough removal, the value of the total surface energy (gamma(s)) and particularly of its polar component, increased considerably and reached the classical polysaccharide figures of gamma(d)(s) similar to 30 and gamma(p)(s) similar to 30 mJ/m(2). The characterization of the impurities by gas chromatography/mass spectrometry analysis indicated the presence of significant amounts of higher alkanes, fatty acids, and alcohols and sterols.