A comarison has been made of the cardiovascular, bronchodilatory, spasmogenic, hyperglycemic, and adrenal-stimulating effects of arterenol, epinephrine, and isopropyluterenol in equivalent dose levels. Epinephrine is twice as potent as arterenol in producing vasoconstriction of the vascular bed of skeletal muscles. Epinephrine acts like arterenol to produce the vasopressor, and Like isopropylarterenol to produce the vasodepressor effect. Isopropylarterenol is three times more effective than epinephrine in prevention of histamine-induced bronchospasm in guinea pigs, while arterenol is 1/60 as effective as epinephrine. Arterenol, like epinephrine, causes contraction of isolated guinea pig's seminal vesicle, but is less active. Isopropylarterenol is devoid of a spasmogenic action. The hyperglycemic activity of arterenol is greater than that of isopropylarterenol, but less than that of epinephrine. They are equally influential on the ascorbic acid metabolism of the adrenals.