Anti-DNAse B test was performed with microtechnique in 160 subjects including patients with acute streptococcal pharyngitis, rheumatic fever and rheumatic heart disease as well as normal controls. It was shown that the antibody titer varied with age, stage of rheumatic fever and rheumatic heart disease as well as the frequency of benthazine penicillin injections. It was also shown in this study that the school children group had considerably higher geometric mean antibody titer than the adult group. The upper normal limit of anti-DNAse B titer was 240 units in the school children group and 160 units in the adult group. The anti-DNAse B test shows a higher positive detection rate for streptococcal infection than ASO, especially when these two tests are used in combination. In patients with manifestations of acute rheumatic fever without elevation of ASO titer, anti-DNAse B test will be of great diagnostic value.