SummaryThe intravenous circulatory activity of the following phenylpropylamines was compared with that of corresponding phenethylamine derivatives and epinephrine in atropinized dogs anesthetized with pento-barbital sodium : y- (3,4-dihydroxyphenyl) -N-Ketopropylamine (I); y- (4-hydroxyphenyl) -N-Ketopropylamine (IV); y-(4-hydroxyphenyl) - y - hydroxypropylamine (VI); N-phenyl-y-ketopropylamine (VIII); N-phenyl-N-hydoxypropylamine (XII); y- (4-methoxy-phenyl)-y-Ketopropylamine (VII); N-(3,4-dimethoxyphenyl) -N-Ketopropylamine (III). These derivatives all were found to exhibit some degree of pressor activity. The above listing is in the order of their decreasing pressor effectiveness. The most active compound (I) manifested 1/100-1/200 and the least active agent (III) possessed < 1/5000 the activity of epinephrine.