The existence of autoantibodies is characteristic of several rheumatic diseases and indicates impaired self-tolerance. The analysis and detection of these autoantibodies represent an important factor in the diagnosis of rheumatic diseases. Immunofluorescence is an important technique in basic science and also one of the most commonly used techniques for the characterization of autoantibodies in clinical medicine thus facilitating the diagnosis and evaluation of rheumatic diseases. Addition of serum samples from individual patients to an antigen substrate (present in fixed cells or tissue) results in a specific reaction between the autoantibodies and the respective antigens. Incubation with a second, fluorescence-linked, anti-human antibody which binds to the primary antigen-bound autoantibodies from patient serum results in fluorescence patterns which are characteristic of certain rheumatic diseases.