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Pressor amines can be formed by the decarboxylation of amino-acids. Dopa decarboxylase is a mammalian enzyme which catalyses a reaction of this type, the formation of P- Two new substrates of the enzyme are described in this paper, namely, 2: 5-dihydroxyphenylalanine and meta-tyrosine (m-hydroxyphenylalanine). Both these amino-acids give rise to pressor amines on decarboxylation, and some of the properties of these amines are also described. The preparation of the tissue extracts and the plan of the manometric experiments differed in no way from the methods already described (Blaschko, 1942). Two organs known to contain dopa decarboxylase were used, the rat's liver and the guinea-pig's kidney. The latter organ gives extracts. with high enzymic activity. The amino-acids were incubated with the tissue extracts in an atmosphere of,nitrogen at a temperature of 37.5°.The pressor action of the amines formed was studied on the arterial blood pressure of the spinal cat. DL-meta-tyrosine was kindly prepared by Dr H. R. Ing by the method described by Blum . Neuberger (1948). We are grateful to him for a sample of the racemic product, as well as of the two stereoisomers. He also gave us a sample of 2: 5-dihydroxyphenylethylamine hydrochloride; this is also a new substauce.

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