An expt. designed to test dominance as a possible modifying factor of aggression caused by frustration. A flock of goats containing several age groups was used. After the dominance organization was detd., the effect of delayed feeding and of recent feeding on the amt. of fighting between each pair was observed. The degree of dominance between each pair was graded. More than 1/5 of the relationships were entirely peaceful under ordinary conditions. The degree of dominance appears to be inversely proportional to the amt. of fighting. The relationship between older and younger animals is definitely correlated with dominance, the older animals being dominant in 47 out of 50 cases. The dominance relationships between [female][female] appear to be approx., but not entirely, the same in cases of sexual frustration as in food frustration. Delayed feeding increases the amt. of aggressive fighting in dominant animals, and recent feeding decreases the amt. of aggression in dominant animals. Delayed feeding causes subordinate animals to take more punishment and thus lower the degree of dominance, but almost never causes aggression in them. These conclusions also apply to animals which are subordinate in one relationship and dominant in another. It may be concluded that dominance strongly modifies the effect of frustration in causing aggression. Hence it may be said that frustration causes aggression in situations in which animals are in the habit of being aggressive. Some possible applications to human affairs are discussed.