Antinuclear antibodies are directed against different nuclear antigens such as deoxyribonucleic acid, ribonucleic acid, nucleoproteins, histones and non-histones-antigens. The importance of ANAs in the characterization of different systemic rheumatic diseases, e.g. autoimmune diseases, has been recognized. The most commonly used assay for ANAs is indirect immunofluorescence. Several methods, such as radioimmunoassays, double immunodiffusion in agarose gel, counterimmunoelectrophoresis or immunoblotting, have been developed and serve to identify antibodies of different specificities. This overview describes the clinical importance of ANAs with reference to the methods of detection. The immunologic diagnosis aspect of different autoimmune and collagen diseases is presented.