A prospective study was conducted to investigate the rate of group A streptococci (GAS) carriers and associated anti-streptolysin O (ASO) titers in serum samples in asymptomatic school children in spring in Duzce, Turkey. Pharyngeal swabs were obtained to detect the presence of GAS and blood samples were collected to determine elevated ASO titers in serum. A total of 351 asymptomatic primary school children were included in the study, and 91 (25.9%) of these were found to be GAS carriers. Of the 91 carrier students, ASO titers were elevated (> or =200 IU/ml) in 34 students (37%). Of the 260 non-carrier children, ASO titers were found as elevated (> or =200 IU/ml) only in 27 (10.3%) students. The difference between the ASO-positivity rate of the GAS carrier group (34 in 91 students) and that of the non-carrier group (27 in 260 students) was found to be statistically significant (P < 0.05). The finding of the significant relationship between ASO positivity and GAS carriage indicated that ASO measurement might be used together with throat culture to identify of GAS carriers.