Notwithstanding the fact that pharmacological studies on the ligamentum teres uteri of various animals have been pretty thoroughly made by a number of research workers, little is known about the human round ligament. The present paper deals with the results of study on the round ligament of the human uterus for the purpose of investigating the automatism and innervation of the ligament, together with the reactions of the organ to drugs. The following results have been obtained by the author's investigation. 1) The round ligament of the human uterus shows rhythmical spontaneous contraction when examined by Magnus' method. 2) Diseases of the uterus, such as adhesion, myoma and, in their early stages, carcinoma and syncytioma malignum, do not hamper the automatism of the round ligament belonging to the uteri so affected, but a round ligament of a somewhat advanced carcinomatous uterus and an atrophied ligament show weak and irregular automatism. 3) The difference in age in patients between 20 and 59 years is not a factor in the automatism of the round ligaments. But ligament of a multiparous uterus produces more active contraction than of one that is nulliparous. 4) Adrenalin exerts either stimulative or depressive effect on the round ligament, according to the degree of its concentration, by affecting the sympathetic nerve. This fact proves that the round ligament of the human uterus is innervated by both the motor and inhibitory fibres of the sympathetic nerve. 5) A small or moderate quantity of pilocarpin causes stimulative action in the round ligament by affecting the parasympathetic nerve, while a large quantity of this drug leads to inhibition, owing to the stimulation of the sympathetic inhibitor. So, it may be seen that the human round ligament is innervated by the parasympathetic nerve which is motor in its function. 6) Acetylcholin exerts stimulative action on the round ligament by affecting the parasympathetic nerve, but in very large quantity it causes the paralysis of the muscle of the ligament. The former justifies the view as to the parasympathetic innervation of the ligament. 7) The action of atropin on the round ligament is uncertain. It is ineffective in some cases, while a stimulative or depressive effect is manifested in other cases. A small quantity of atropin paralyzes the parasympathetic nerve and a somewhat larger quantity causes the paralysis of the motor sympathetic. Very large dose results in the paralysis of the muscle. 8) Pituitrin, in low concentration, produces a stimulative effect on the round ligament by stimulating the motorsympathetic, while a moderately concentrated solution causes either stimulation, by affecting both the motorsympothetic and the muscle itself, or inhibition, owing to the stimulation of the sympathetic inhibitor. In high concentration it causes the paralysis of the muscle, which may be attributed to the effect of chloretone. 9) Bombelon manifests depressive action on the round ligament by acting on the inhibitory fibre of the sympathetic nerve. 10) Nicotin exerts stimulative or depressive effect on the round ligament by stimulating either the motor or inhibitory fibres of the sympathetic nerve. The effect of a small quantity is mainly stimulative, while in moderate quantity it is likely to cause inhibition. A large quantity of this drug affects the muscle, resulting in its paralysis. 11) A small quantity of cocain produces stimulative action on the round ligament by stimulating the motorsympathetic, and a moderate quantity affects the muscle also. A large quantity paralyzes the muscle. 12) Comparing the results above mentioned with those seen in the human uterine musculature, it may be said that adrenalin, pituitrin, bombelon and nicotin cause somewhat different reactions in those two organs, while pilocarpin, acetylcholin, cocain and barium exert the same effect on both of them, but a more active effect on the round ligament than on the uterus. Atropin shows the same effects in both.