1. The question whether the rabbit's spectral sensitivity curve is based on one spectral system or based on more systems is investigated. 2. For this purpose two different methods have been applied. The first method is a photometric match technique that made use of moving contrasts. Lack of eye movement was the indicator for an achieved brightness match. The second method was a threshold measurement in an automatically operated two-choice apparatus. 3. The first method resulted in sensitivity curves that suggested the existence of a ‘blue sensitive’ system and a ‘green sensitive’ system. In the second method chromatic adaptation probably resulted in depression of sensitivity of the ‘blue sensitive’ system thus separating the ‘green sensitive’ system.