Tyramine, an important plant intermediate, was found to be a substrate for two proteins, a copper amine oxidase and a peroxidase from Euphorbia characias latex. The oxidation of tyramine took place by two different mechanisms: oxidative deamination to p-hydroxyphenylacetaldehyde by the amine oxidase and formation of di-tyramine by the peroxidase. The di-tyramine was further oxidized at the two amino groups by the amino oxidase, whereas p-hydroxyphenylacetaldehyde was transformed to di-p-hydroxyphenylacetaldehyde by the peroxidase. Data obtained in this study indicate a new interesting scenario in the metabolism of tyramine.