The NS1 and NS2 proteins of human respiratory syncytial virus (RSV) were expressed using baculovirus. Antisera to these expressed proteins and to synthetic peptides were raised in rabbits and used to characterise the proteins. Multiple forms of both NS1 and NS2 proteins were detected in RSV infected cells by both immunoblotting and radioimmunoprecipitation when non-reducing, but not reducing, conditions were used. In pulse-labelling experiments the monomeric form of NS1 was stable, while that of NS2 was unstable with a half life of about 30 min. The NS1 protein associated with the matrix (M) protein and could be co-precipitated by a monoclonal antibody to M protein. The NS2 protein did not show any detectable association with RSV structural proteins. These results indicate that the NS1 and NS2 proteins have distinct roles in the viral life cycle.