Attempted to find the equivalent brightness for red to the light-adapted eye of the rabbit. This work was done with the Bradley colored papers, and the Hering gray and black papers. The apparatus consisted of a wooden box divided into 2 compartments, having doors with a red paper on one and a grey paper on the other. Tests on binocular vision were conducted. The observations on 5 rabbits has been given in detail. Results show that the rabbits could discriminate Bradley saturated red paper from Hering grey, which was based on brightness, rather than on color, differences. Hering black appeared darker to the rabbit than Bradley saturated red. Red had a low stimulating effect on the rabbit's retina. The rabbits were guided by visual clues in acquiring a habit. Evidence indicated that while the rabbit is capable of binocular vision, it uses monocular vision in preference. (PsycINFO Database Record (c) 2006 APA, all rights reserved)