In about 80 per cent of ARF patients, ASO titre is significantly raised. ASO titres vary with age, geographical area and other fevers, which influence frequency of streptococcal infection. ASO titres are at peak usually 2-3 weeks after the streptococcal infection and fall rapidly in the next few months. Acute polyarthritis usually coincides with peak of ASO titre. Hence if ASO titre is normal in presence of arthritis, possibility of ARF is less. Anti-Dnase B and anti-hyaluro-nidase levels are important indicators of recent streptococcal infection.