The determination of antistreptolysin O (ASLO) and antideoxyribonuclease B (ADNase B) was carried out on a sample of 199 sera from normal subjects and on a sample of 4019 sera from patients admitted to the Strasbourg University Hospital Center. The sera of hospital origin were divided into two groups. The first group (n = 3889) consisted of sera taken at random, the second group (n = 130) corresponded to patients in whom we isolated a streptococcus of group A. The results obtained show that the distribution of ADNase B and ASLO of normal subjects follow a logarithmic distribution. The geometric averages of the titres DNAase B and ASLO of normal sera and of the first group of hospital origin are scarcely different, whereas the geometrical means of the titres of the second group of sera of hospital origin are quite different and two or three dilutions higher. We noted that the titres of DNAase B and ASLO were in agreement in 84% of cases in the whole group of hospital sera. Among the cases of discrepancy, the negative ASLO and the positive DNAase B corresponded mainly to streptococcal infections.