Infection of different human epithelial cell lines with human respiratory syncytial virus (HRSV) revealed significant differences in the electrophoretic mobility of the viral attachment glycoprotein (G). Cell-type specific differences in G protein glycosylation were observed with certain lectins and sugar-specific reagents. Furthermore, substantial changes in the reactivity of the G glycoprotein with anti-G monoclonal antibodies were associated to the infected cell type. Strain-specific epitopes--present in a limited number of HRSV isolates of the same antigenic group--were particularly susceptible to cell-type-specific modifications of the mature G protein. Some of these epitopes, which were either exposed in the unglycosylated precursor or reproduced with synthetic peptides, were nonetheless masked in the mature G protein expressed in certain cell lines. Antigenic and electrophoretic mobility changes of the G glycoprotein were reverted in extracts of HEp-2 cells infected with HRSV grown in other cell types, indicating that phenotypic traits rather than selection of variants were associated to the above stated changes. These results highlight the importance of cell-type-specific modifications for HSRV G glycoprotein antigenicity and raise questions about the actual antigenic structure of this molecule when HRSV replicates in the respiratory tract.