Delivery of the rhinovirus genome into the cytoplasm involves a cooperative structural modification of the viral capsid. We have studied this phenomenon for human rhinovirus serotype 2 (HRV2). The structure of the empty capsid has been determined to a resolution of better than 15 A by cryo-electron microscopy, and the atomic structure of native HRV2 was used to examine conformational changes of the capsid. The two proteins around the 5-fold axes make an iris type of movement to open a 10 A diameter channel which allows the RNA genome to exit, and the N terminus of VP1 exits the capsid at the pseudo 3-fold axis. A remarkable modification occurs at the 2-fold axes where the N-terminal loop of VP2 bends inward, probably to detach the RNA.