The kinetics of the group A specific polysaccharide antibody were studied in children with acute rheumatic fever who had no carditis, children with acute rheumatic fever who had carditis and developed rheumatic heard disease and in children with acute poststreptococcal glomerulonephritis. The children with rheumatic fever who had carditis and those who did not, were kept on continuous antistreptococcal prophylaxis. In the group of children who developed rheumatic heart disease the titer of the antibody at onset was significantly higher than those who had rheumatic fever but no carditis (P = 0.01). After a mean follow-up period of three years, a high titer was maintained in children who developed rheumatic heart disease only and was significantly higher than that found in children with rheumatic fever who had no carditis (P = 0.001) and in children with poststerptococcal nephritis (P = 0.001).