A commercial, branched polyethyleneimine was analyzed by13C-NMR. The chemical shift assignments for the eight principal peaks were compared to the calculated chemical shifts using an additivity relationship developed for low molecular weight acyclic aliphatic amines. The change in carbon chemical shift induced by H/D exchange at nearby nitrogens was examined for this polymer and low molecular weight model compounds. The direction and magnitude of the shift are determined by the number and proximity of exchangeable NH' and are described by a simple formula. The spin lattice relaxation times for the various methylenes indicate the usual decreasing mobility for units at chain ends, internal units, and units close to branch points in that order. The integrated spectrum, under equilibrium conditions, is not consistent with the reorted amine distribution, 1°:2°:3° = 1:2:1. Our results indicate 38k l°, 36% 2°, and 26% 3°.