The degree of poIymerization (DP),' which measures the number of monosaccharide units per molecule, is generally used to express the size of an oligosaccharide. For reducing oligosaccharides, the widely used methods of determining DP are based on t'he assay of reducing end groups. However, these methods normally involve chemical transformations which may give rise to unsatisfactiory features (I). In the course of preparing N-acetyl chitooligoses from t'he hydrolyzatc of chitin, it was found that chrom&ographic techniques used primarily for the purification of oligosaccharides (2, 3) could be adapted to determined simultaneously the size and the purity of N-acetyl chitooligosea. This paper describes the determination of DP of N-ncctyl chitooligoscs ?)y Sephadex permeation, thin-layer, and gas chromatographic methodti. Materials. Chitin was purcha~etl from Sigma Chemical Co. N-Acetyl-D-glucosamine (2-acetamido-2-deoxy+glucose? NAG) and Tri-Sil were obtained from Pierce Chemical Co. Sephadex Gl5 and G25 were purchased from Pharmacia F'ine Chemicals and silcia gel G from Research Specialties Co. Neopentyiglycol sebacate polyester and non-acid-washed Chromosorb W (80-100 mesh) were obtained from Chromafographic Specialties. Di-N-acetyl chitobiose, which had m.p. 251-252.5"C and [l~]D +17.3 (cl.0 water, at' equilibrium), tri-N-acet,yl chitotriose, which has [(Y]D +1.5 (cl.0 water, at eyuilib,rium), tetra-LV-acrtyl chitotetraose, which had [a] n -2.6 (cl .O water, at cqui1ibrium) , pent a-N-acetyl chitopentaose, which had [aID -6.3 (cl.0 water, at equilibrium), and hexa-N-acetyl chitohexaose were prepared and purified by t.he procedure described by Rupley (3). N-Acetylglucosaminol (2-acetamido-2,-deoxy-n-glucitol,