Human colour vision is mediated by three light-sensitive pigments, each found in a different cone-cell type. The absorption spectra of the human cone pigments have been sought for over a century using techniques such as psychophysical colour matching, reflection densitometry, electroretinography, single-cell action spectra and, most directly, microspectrophotometry. We report here a direct determination of the human cone pigment photobleaching difference absorption spectra after the production of each cone pigment apoprotein in tissue culture cells transfected with the corresponding complementary DNA clones. The mean values for the wavelength of maximal absorption are 426 nm for the blue pigment, 530 nm for the green pigment, and 552 nm and 557 nm for two polymorphic variants of the red pigment.