Abstract
The results of immunofluorescence studies in nine cases of rheumatoid arthritis and nine cases of ankylosing spondylitis are presented. Antiglobulin activity was sought with fluorescein labelled, heat aggregated human IgG and rabbit immunoglobulin (indirect immunofluorescence). A similar degree of increased staining for rheumatoid factor activity was seen after pepsin digestion in all cases of rheumatoid arthritis and three of the ankylosing spondylitic cases. This staining for rheumatoid factor could also be shown in control tissue after pepsin digestion, suggesting that the enhanced staining was an artefact.