A total of 13 respiratory syncytial (RS) virus specific polypeptides were identified by pulse-chase metabolic labeling of infected HEp-2 cells. Ten of the 13 proteins were shown to be unique. They were the L, G, F (F1, F2), N, P, M, 24K, 14K, 11K and 9.5K proteins. These conclusions were based on peptide mapping and on previous work showing that each of 10 polypeptides are coded for by a unique mRNA. The seven largest proteins, L, G, F (F1, F2), N, P, M and 24K were identified clearly as virion structural proteins. The 24K protein was characterized by detergent and salt dissociation studies as an envelope-associated protein, bringing to four (G, F (F1, F2), M and 24K) the number of membrane associated proteins for RS virus. A fourth membrane-associated protein has not been described previously for any other paramyxovirus. Of the three smallest proteins, the 14K and 11K were characterized as non-structural proteins. The 9.5K protein was detected in low amounts in highly purified preparations of virions.