Nuclear-pore complexes (NPCs) span the nuclear envelope and mediate bidirectional transport between the nucleus and cytoplasm. Macromolecules (>40 kDa) require transport receptors to transit the NPC efficiently, whereas smaller molecules diffuse through the NPC passively. The mechanism through which the semipermeable barrier at the center of the NPC regulates selective transport is unknown. Aiming to elucidate this mechanism, Yang and colleagues have investigated spatial cargo distribution within the NPC² by using single-point edge-excitation subdiffraction (SPEED) microscopy.