This chapter concentrates on analogues in which methyl groups have been deleted from the polyene side chain and on analogues in which the polyene side chain has been truncated. These analogues have proved to be particularly useful for the control of various aspects of rhodopsin function. The chromophore of the G protein-coupled receptor (GPCR) rhodopsin demonstrates a remarkable ability to control the activity of that receptor. When the pigment is in its regenerated state as rhodopsin, the chromophore is acting as an inverse agonist, locking the receptor in its inactive state. If the chromophore-binding pocket is vacant, the apoprotein shows a low level of activity, which is eliminated on the formation of pigment. The action of a single photon of light is to isomerize a double bond in the chromophore, converting the compound into an agonist. The agonist results in the movement of receptor to its active conformation by inducing protein conformational changes and forming a binding site for the G protein.