Dextran fractions from NRRL strains Leuconostoc mesenteroides B-1299 and B-1399, and the native, structurally homogeneous dextrans from L. mesenteroides. B-640, B-1396, B-1422, and B-1424, were examined by 13C-n.m.r. spectroscopy at 34 and at 90°, and by g.l.c.-m.s. The 13C-n.m.r. data indicate that the dextrans of this series branch exclusively through α- d-(1→2)-linkages, and differ from one another only in degree of linearity. Diagnostic, 13C-n.m.r resonances, correlating with 2,6-di- O-substituted α- d-glucosyl residues at branch points, have chemical shifts that are independent of the degree of linearity of the dextran. The intensities of these diagnostic resonances from branching residues, compared to the resonances associated with linear dextran (low degree of branching), are generally proportional to the degree of branching established by methylation-fragmentation analysis. The validity of assignment of the diagnostic, 13C-n. m.r. resonances is substantiated by a critical review of methods previously used to provide structural information on dextrans having α- d-(1→2)-linkages, and by evaluation of the corresponding results on the basis of the ultimate standard-methylation structural analysis.