A modified and improved jumping apparatus is used to test color discrimination in rats. 36 rats in all were used in the various tests. The animals were taught to discriminate between pairs of colored lights that were approximately equivalent in brightness for the observer; the point of subjective equality for each rat was detd. and learning of the color discrimination then began. The animals distinguished red-blue, red-green, red-yellow, and blue-yellow on the basis of hue difference. The animals were unable to discriminate blue-green and green-yellow on a similar basis.