The microstructure of chitosan, a linear copolymer of glucosamine and N-acetylglucosamine units widely used in biomedical applications, is closely dependent on the conditions of its preparation. Knowledge of the structural differences between chitosan preparations is very important in determining the properties of chitosan and essential for structure-activity analysis where biological systems are concerned. Determination of the pattern of acetylation of chitosan samples (P(A) parameter) by (13)C NMR spectroscopy hitherto required depolymerization of the native chitosans. The present study has demonstrated that this step is not necessary for determining P(A) of low-molecular-weight chitosan samples.