Mutants of a non-glycosylated strain of SA 11 rotavirus (clone 28), were selected using a monoclonal antibody directed against the VP 7 protein. These mutants possessed an amino acid substitution at residue 238 of VP 7, whereas mutants of wild type SA 11 selected with the same antibody have previously been shown to contain a substitution at residue 211 (i.e., in the antigenic C region). In both cases the mutations produce new potential glycosylation sites, and these were found to be utilized. The mutations also lead to gross antigenic changes, and these were found to be reversible upon removal of the attached carbohydrate. The results suggest an important role for carbohydrate in influencing the exposure of antigenic determinants of the rotavirus serotype-specific protein, VP 7.