Facial expression in anger was studied experimentally with a monkey. The choice of the subject was based on the following reasons:(I) Since the object of the study aimed at getting as pure a native expression as possible, human adults were thought unsuitable. (2) Human infants were impossible to get due to two requirements imposed on, which were that no attendant was allowed, and that the child was to be excited to anger. (3) A monkey is relatively free in its emotional expression from environmental influence and also from suggestion. (4) The facial musculature of a monkey is almost identical with that of man. A Macacus cynomologous female owned by D:. Tinklepaugh, Yale University, was excited by two anger stimuli, and snap-shot pictures were taken. Fig. 3 shows “Psyche” threatened by a stranger with a stick. Fig. 4 shows “Psyche” challenging a dummy bear. The characteristic expression of anger here shown is that opining of the mouth, widening of the nostril, exposure of the teeth, frowning of the forehead. These features of expression are indicative of the circulatory and respiratory responses in preparation for a fight. Hence it was concluded that the native human facial expression in anger originates from circulatey and respiratory responses in preparation for a fight, and has a phylogenetic significance.