The theory of focal infection was influenced by advances of bakteriology at the beginning of the last century. It proposed tkat circumscribed chronic infectious foci in the macroorganism could result in diverse systemic diseases. Surgical elimination of the foci became the standard procedure in many branches of medicine. Many thousands of patients esere subjected to tooth extractions, tonsillectomies and other interventions without the benefit of these procedures being proved by suitable studdis. The connection between the systemic disease and the local infection can be considered proved e.g. in rheumatic fever after streptococcal nasopharyngitis, in Reiter's syndrome (after urogenital infection caused by chlamydiae or after intestinal infection caused by salmonellae or shigellae) or after the intestinal infection by the serotype 0157:H7 of Escherichia coli. Recently, a number of possible relations has been described between the infection by certain microorganisms and e.g. rheumatoid arthritis (Proteus mirabilis) or active ankylosing spondylitis (Klebsiella pneumoniae), or between the infection of periodontal tissues and such diverse conditions as myocardial infarction or preterm delivery. None of the studdis has yet proved causal relationship between the infection and the respective disease.

        Key words: focal infection - history - arthritis - rheumatic fever - periodontitis - endocarditis - id eruptions - Guillain-Barré syndrome.