THE REASONS certain children have rheumatic fever and why clinical manifestations and course of the disease vary so widely in children and adults who have the disease are unknown. Evidence has increased rapidly to indicate that Group A hemolytic streptococci, or the soluble antigens produced by them, precipitate the onset of the disease.1 The part host factors play in the course of rheumatic fever is not clearly understood. Variation in the incidence and manifestation of the disease at different age levels indicate certain host differences. During mid-childhood the incidence of rheumatic fever is at a maximum and is characterized by carditis. Although rheumatic fever is found rarely in children under 4 years of age, its occurrence is accompanied generally by a more severe carditis. The incidence of clinically recognizable rheumatic fever is highest in children living in adverse environmental situations, but what and how factors associated with poor living