The present invention is based on the in vivo demonstration that RSV and PIV can be inhibited through intranasal administration of RNAi agents as well as by parenteral administration of such agents. Further, it is shown that effective viral reduction can be achieved with more than one virus being treated concurrently. Based on these findings, the present invention provides general and specific compositions and methods that are useful in reducing RSV or PIV mRNA levels, RSV or PIV protein levels and viral titers in a subject, e.g., a mammal, such as a human. These findings can be applied to other respiratory viruses.