Retinal induction was studied in normal and color-defective subjects by means of Motokawa's method. 1. The effect of light in terms of ζ was investigated with spectral lights, and it was found that the ζ value for red lights was dicidedly small in a protanomalous. 2. ζ-time curves for spectral lights were found much different from those of the normal. The curve for blue-green light was the same as the curve for white light. This fact may be correlated with the situationn that the light of 480-490mμ looked to the subject as gray. The curves for yellow and blue were found similar to those of the normal. 3. The two parts of the spectrum, blue-green and red caused no retinal induction in the protanomalous. Lights of yellow and yellow-green were more effective to cause retinal induction in the color-defective than in the normal. Blue light was found equally effective in both cases. 4. Effectiveness of spectral lights for retinal induction was investi-gated systematically, plotting contrast effects as ordinates against the wave-lengths of inducing spectral lights as abscissas, and it was found that orange and blue-green are optimal in the normal, while blue and yellow-green are favorable in the protanomalous.