Familial Mediterranean fever (FMF) is an autosomal recessive disorder. Although the pathogenesis of the disease is not yet completely understood, enhanced acute-phase responsiveness is considered to be one of the most important mechanisms. The presence of high levels of antistreptolysin O (ASO) antibodies and streptococcus-associated diseases, such as acute poststreptococcal glomerulonephritis (AGN) and acute rheumatic fever (ARF), has been reported in patients with FMF. In order to better understand the effect of FMF on antistreptococcal antibody response, we measured ASO and antideoxyribonuclease B (anti-DNAse B) levels in patients with FMF and compared them with those in healthy controls. The study consisted of two parts. In the first step, antistreptococcal antibody levels were analysed in 44 patients with FMF and 165 healthy children who had no history or clinical evidence of upper respiratory tract infection (URTI) for the last 4 months. In the second step, antistreptococcal antibody levels were measured in 15 patients with FMF and 22 healthy controls in response to documented group A β-haemolytic streptococcal pharyngitis. In the first part of the study, ASO and anti-DNAse B levels in patients with FMF were found to be significantly higher than those in healthy controls (P<0.001). In the second part, ASO and anti-DNAse B titres were found to be significantly higher in patients with FMF than in controls (P<0.001 and <0.05, respectively) 4 weeks after a positive throat culture. We concluded that patients with FMF have an exaggerated response to streptococcal antigens and might be prone to poststreptococcal non-suppurative complications, such as ARF.