In a first experiment, groups of deuteranopes and protanopes were characterized psychophysically by the slopes of regression lines fitted to yellow intensity settings from their Rayleigh matches. In a second experiment, color normal male subjects were characterized by their 2 and 8 deg Rayleigh match points. All subjects had been previously characterized genetically by the presence of the amino acid serine or alanine at position 180 on their L cone or L/M hybrid opsins. Dichromats and color normal subjects with serine had greater sensitivity to the red primary than did those with alanine. Calculations based on psychophysical results suggest that the substitution of serine by alanine in the L cone opsin or L/M hybrid opsin produces a shift in lambda(max) of the expressed pigment toward shorter wavelengths by an amount varying between 2.6 and 4.3 nm, with the shifts in lambda(max) for the dichromats being larger than those for the color normal subjects.