Nuclear import and export of viral nucleic acids is crucial for the replication cycle of many viruses, and elucidation of the mechanism of these steps may provide a paradigm for understanding general biological processes. Influenza virus replicates its RNA genome in the nucleus of infected cells. The influenza virus NS2 protein, which had no previously assigned function, was shown to mediate the nuclear export of virion RNAs by acting as an adaptor between viral ribonucleoprotein complexes and the nuclear export machinery of the cell. A functional domain on the NS2 with characteristics of a nuclear export signal was mapped: it interacts with cellular nucleoporins, can functionally replace the effector domain of the human immunodeficiency virus type 1 (HIV‐1) Rev protein and mediates rapid nuclear export when cross‐linked to a reporter protein. Microinjection of anti‐NS2 antibodies into infected cells inhibited nuclear export of viral ribonucleoproteins, suggesting that the Rev‐like NS2 mediates this process. Therefore, we have renamed this Rev‐like factor the influenza virus n uclear e xport p rotein or NEP. We propose a model by which NEP acts as a protein adaptor molecule bridging viral ribonucleoproteins and the nuclear pore complex.