Abstract: A process and device are disclosed for carrying out in particular quantitative fluorescence immunity tests by means of evanescent field excitation, possibly on the basis of various known biochemical assays of systems generally composed of receptor-ligands. However, antibody-antigen systems are preferably evaluated. The invention should enable quantitative fluorescence immunity tests with various known biochemical assays to be carried out with a very simple device. For that purpose, a light source is used which emits rays of an almost monochromatic light having a wavelength which causes a marking substance bound to the antibody to become fluorescent.