[Skin tests with phytohaemagglutinin (PHA). Correlation with other parameters of cell-mediated immunity (author's...

100 healthy persons were investigated to find out whether there is a correlation between a lymphocyte stimulation (3H-thymidine incorporation in the lymphocyte transformation test) with phytohaemagglutinin, pokeweed mitogen and concanavalin A and the in vivo reactivity to intracutaneous phytohaemagglutinin application (measured as medium diameter of infiltrates). Further we searched for an influence of positive or negative reactivity to the specific antigens trichophytin, candidin and streptokinase-streptodornase. 1. There is a good qualitative correlation in normal persons between in vitro lymphocyte stimulation by phytohaemagglutinin, pokeweed mitogen and concanavalin A and the medium diameter of infiltrates after intracutaneous application of 2 mug phytohaemagglutinin. Using lower doses of phytohaemagglutinin no such correlation could be found. A quantitative correlation between the medium diameter of infiltrates and lymphocyte transformation by phytohaemagglutinin and pokeweed mitogen cannot be demonstrated. For concanavalin A there is a negative correlation significant at the 99% level. 2. In vivo reactivity to phytohaemagglutinin does not differ in persons with negative and positive reactions to the specific antigens. 3. Lymphocyte stimulation by phytohaemagglutinin, pokeweed mitogen and concanavalin A of persons with positive reactions to trichophytin, candidin and streptokinase-streptodornase is significantly greater than in those with negative reactivity. 4. The results indicate in vivo phytohaemagglutinin testing as a good screening method to judge cell-mediated immunocompetence. The general applicability for differentiation of immunodeficient and immunocompetent patients is to be further investigated.