Determination of peripheral lymphocytes has increasing importance in laboratory examinations. However, evidence concerning differential diagnosis is low. For experimental questions and therapeutical monitoring application of this method is more distributed. This paper transfers practical experiences concerning the detection of cellular surface antigens. For the investigations, monoclonal antibodies from the Karl-Marx-University Leipzig were used in immunofluorescence microscopy. Limits of the test are demonstrated (in skin diseases and HIV-infection f.e.).