A new method for the estimation of 4-hydroxy-3-methoxyphenylethylamine (3-methoxytyramine) in brain tissue is described. This is based on the formation of a fluorescent derivative by oxidation with potassium ferricyanide in ammonium hydroxide solution.2. The effects of some drugs on the concentration of 3-methoxytyramine in the brain are reported.3. The significance of changes in the striatal concentration of 3-methoxytyramine is discussed.