Eight separate monoclonal antibodies to the Long strain of respiratory syncytial virus (RSV) were tested for their utility as rapid diagnostic reagents in immunofluorescence. Preliminary screening indicated that all 8 reacted with 11 field strains from three previous local RSV outbreaks and with 4 of 5 additional strains chosen because of their antigenic diversity by neutralization. Two monoclonal antibodies, one each directed against a surface glycoprotein and the nucleocapsid protein, were then compared, singly and combined, with a polyclonal antiserum as diagnostic reagents in 209 consecutive samples submitted to our diagnostic laboratory. Agreement between the two monoclonal antibodies was 100% and between them and the polyclonal serum was 98%. Sensitivity in relation to culture was 96-98%. Monoclonal antibodies are excellent immunofluorescent diagnostic reagents; antigenic diversity among RSV strains was not an impediment to their use in this study.