French chemist Auguste Millon developed Millon's test (thus the name) that can detect phenolic compounds, such as tyrosine. In this test, a reagent containing mercuric nitrate dissolved in nitric acid (called Millon's reagent) is added to the test solution, and then heated. A red solution or precipitate that forms in heating is an indication that tyrosine is present (a positive result).
Since tyrosine is an amino acid occurring in nearly all proteins, Millon's test is used for detecting proteins. Therefore, proteins without tyrosine residues cannot be detected using this test. Thus, other tests (e.g. biuret test) to confirm presence of proteins may be necessary.
Millon's reagent is toxic and dangerous when its fumes are inhaled. Take caution in handling this reagent when performing this test.