Crystallization of 2-glycosyl-1,3-dihydroxy-4,4,5,5-tetramethylimidazolidine under aerobic conditions gives rise to single crystals which contain a small amount of the 2-glycosyl-3-hydroxyimidazolidin-1-oxyl radical. Hyperfine coupling tensors with the nitroxide nitrogen, a -proton, and a -nitrogen are obtained. The anisotropic coupling constants for the -proton are larger than those calculated for a nitroxide in a planar conformation.