The eukaryotic nucleus is surrounded by a protective nuclear envelope, which is perforated by trafficking machines termed nuclear pore complexes (NPCs). The NPCs are the sole mediators of exchange between the nucleus and the cytoplasm. Small molecules pass through the NPCs unchallenged; however, large macromolecules are excluded unless chaperoned across by transport factors. Here, we suggest a model, termed 'virtual gating', to explain the mechanism of this rapid and selective macromolecular trafficking.