This paper describes the occurrence of kernicterus and factors which influence its development in the strain of rats * first studied by Gunn.22,23 The disease of humans designated in 1903 by Schmorl 39 as kernicterus has, in our opinion, not been observed or induced in its entirety in animals. Various workers, however, have demonstrated the toxicity of indirect bilirubin. [12][13][14][15]24,26,[44][45][46]