Two monospecific rabbit antisera to the G glycoprotein, one induced with purified G and the second with a recombinant vaccinia virus containing the gene for G, inhibit the attachment of purified [35S]methionine-labelled Long strain of respiratory syncytial virus to monolayers of HeLa cells. Attachment was not inhibited by monospecific rabbit antisera to glycoprotein F induced with either purified F or with a recombinant vaccinia virus containing the gene for F.