Summary 1.The tuberculin test is a simple and accurate method of determining the incidence of tuberculous infection. 2.The Mantoux or intracutaneous method is the preferable way of performing this test. 3.Interpretation of the reaction should take place 48 hours after the test is performed. 4.The degree of reaction has little significance; therefore, the result should usually be designated as simply positive or negative. 5.A negative test is one which produces no reaction, or at most merely a small area or redness without oedema. 6.A positive test is one which produces a definite reaction with hyperemia surrounding an area of oedema at least 5 mm. in diameter. 7.Aside from a few easily recognized exceptions, a negative tuberculin test is evidence that there is no existing tuberculous infection. 8.A positive tuberculin test is evidence that at least the first infection type of tuberculosis is present. 9.A positive tuberculin reaction denotes a distinct health liability because of danger from: (a)Reactivation of the present lesion. (b)Active tuberculosis from subsequent exogenous infection. (c)Harmful allergic reactions from any tuberculo-protein. 10.Large scale tuberculin tests frequently disclose unsuspected sources of infection. 11.World wide use of the tuberculin test has shown the incidence of tuberculous infection to be much less than was formerly believed.