Respiratory Syncytial Virus (RSV) is an important pediatric infectious agent for which no effective vaccines are available. Elucidation of the RSV replicative strategy is useful in developing and evaluating potential vaccine candidates. We studied the function of two nonstructural proteins of RSV, NS1 and NS2 in a plasmiddependent RSVCAT minigenome model rescue system. We found that concurrent expression of NS1 or NS2 of RSV inhibited the transcription and replication of minigenome analogs in a dosedependent manner as measured by the reduction in CAT activity and CATspecific RNA synthesis. NS1 demonstrated higher levels of inhibiton than NS2 at the intracellular protein levels that are comparable to those in RSV infected cells. Our results provide the first indication of a functional role for these nonstructural proteins in RSV replication and transcription.