Report on two patients whose symptoms suggested the presence of congenital achromatopsia. In one case there was indeed total colour blindness, but a normal photopic ERG. Here, achromatopsia is the present stage in a process of slow functional decay of the central retina. Most probably the underlying disorder is progressive foveal dystrophy, a central form of cone dystrophy. In the other case there was a nonrecordable photopic ERG, but trichromatic colour vision. This appears to be another patient with oligo-cone trichromasy (general cone dysfunction without achromatopsia), as described by Van Lith.