[Rheumatoid factor: study history and concept evolution].

Rheumatoid factor became the first laboratory marker of rheumatoid arthritis and one of the first serological markers used to recognize the major autoimmune diseases. Details of the discovery with special regard to contribution of E. Waaler and H. Rose are presented in this historical review. Same assays used to exam the rheumatoid factor, its frequency and modern view on diagnostic significance in different diseases are described in this article.