The chromatic activity and potency of various sympathomimetic amines were examined in the normal frogs using the Hogben and Slome Index as a simple method for measuring melanophore responses. All the sympathomimetic amines tested in this experiment exhibited the marked aggregation of melanophores. Among these amines, the order of potency in producing the melanophoreaggregation was catecholethylamine derivatives (epinephrine and isoproterenol) monohydroxyphenylethylamine derivative (tyramine) with exception of phenylephrine> nonhydroxyphenyletyhlamine derivatives (ephedrine and propadrine). Of catecholethylamine derivatives, thc melanophore-aggregating activity of epinephrine was more potent than that of isoproterenol. On the other hand, phenylephrine belong to the monohydroxyphenylethylamine derivatives was the least potent agent than the other amines tested.