Background: A similar phototransduction cascade confers different light sensitivity in rods and cones. Results: Rod and cone G␣ t are similar with respect to coupling to visual pigments and light-induced translocation. Conclusion: Rod and cone G␣ t are equivalent functionally. Significance: Reduced sensitivity in cones does not result from reduced coupling efficiency between the GPCR and G protein or a lower concentration of G protein in cones.