G-protein-coupled receptors (GPCRs) are a large family of seven-transmembrane-helix proteins that mediate responses to hormones, neurotransmitters and, in the case of rhodopsin, photons. The recent determination of the structure of rhodopsin at atomic resolution opens avenues to a deeper understanding of GPCR activation and transmembrane signaling. Data from previous crosslinking, spin labeling and scanning accessibility experiments on rhodopsin have been mapped onto the high-resolution structure. These data correlate well and are consistent with the structure, and suggest that activation by light opens a cleft at the cytoplasmic end of the seven-helix bundle of rhodopsin. Furthermore, lessons learned from rhodopsin might also apply to other members of this essential family of receptors. (For an animation of the crystal structure of rhodopsin see http://archive.bmn.com/supp/tips/tips2211a.html)