Abstract: The mechanism of the respiration stimulating action of coramin was studied in anesthetized animals by comparing the respiratory stimulant threshold dose (RSTD) using different ways of administration namely into the vein, into the vertebral artery and into the carotid artery. Cardiazol and lobelin were also studied in the same manner for comparison. The following results were obtained.1. In cats anesthetized With urethane (1 g/Kg, i. p.), the mean intravenous RSTD of coramin was 24.9 mg/Kg, the mean intravertebral about 1/35 (0.7 mg/Kg) and the mean intracarotid about 1/6 (4.3 mg/Kg) of the intravenous dose; the mean intravenous RSTD of cardiazol was 8.5 mg/Kg, the mean intravertebral about 1/4.5 (1.9 mg/Kg) and the mean intracarotid about 1/3 (3 mg/Kg) of the intravenous dose(but there developed respiratory depression instead of respiratory stimulation in some animals when injected intracarotidly); the mean intravenous RSTD of lobelin was 0.5 mg/Kg, the mean intravertebral about 1/10 (0.05 mg/Kg) and the mean intracarotid about 1/8.5 (0.06 mg/Kg) of the intravenous dose.2. In rabbits anesthetized with urethane (1 g/Kg, i. v.), the mean intravenous RSTD of coramin was 40.8 mg/Kg, the mean intravertebral about 1/10 (4.1 mg/Kg) and the mean intracarotid about 1/8 (5 mg/Kg) of the intravenous dose (here developed again respiratory depression in some animals while injected intracarotidly); the mean intravenous RSTD of cardiazol was 14.9 mg/Kg, the mean intravertebral about 1/3 (5 mg/Kg) of the intravenous dose and in the intracarotid injection experiments, most of the animals developed respiratory depression; the mean intravenous RSTD of lobelin was 2.2 mg/Kg, the mean intravertebral about 1/8 (0.3 mg/Kg) and the mean intracarotid about 1/6(0.4 mg/Kg) of the intravenous dose.From the above mentioned experiments, it can be concluded that coramin stimulates the respiratory centre directly. A reflex stimulation by way of the chemoreceptors in the carotid body could only be demonstrated with much larger doses.