The influence of the presence of oligosaccharide branches was examined with respect to the behavior of glycopolypeptides in empirical molecular weight estimation methods in the presence of sodium dodecyl sulfate (NaDod-SO4). This examination was conducted by comparing the gel chromatographic and gel electrophoretic behaviors in the presence of NaDodSO4of 13 glycopolypeptides of known chemical and physical properties to those of regular polypeptides. Errors in the gel chromatographic molecular weight for glycopolypeptides in NaDodS04varied from -22% to + 10% and indicated that the hydrodynamic behavior of the glycopolypeptide-NaDodSO4complex could not be correlated with the amount of carbohydrate in the glycopolypeptide. NaDodSO4binding measurements on a number of the glycopolypeptides suggest that the polypeptide moiety binds the nominal weight ratio of NaDodSO4, while the carbohydrate portion exhibits little or no NaDodSO4binding. As has been reported by others, the polyacrylamide gel electrophoretic behavior of glycopolypeptide-NaDodSO4complexes yielded abnormally high molecular weight estimates. In general, the error of these estimates diminished with decreasing porosity of the gel; however, each glycopolypeptide behaved in a unique fashion. Treatment of the electrophoretic data by any of several empirical means provided no reliable way to correct for the glycopolypeptides’ aberrant behavior. © 1980, American Chemical Society. All rights reserved.