The concentration of streptococcal antihyaluronidase has been measured in the sera of several groups of subjects by an adaptation of turbidimetry to such titrations.

Among presumably normal subjects such titers occur only in very low concentrations in infants, but in higher ranges in new born infants and older children. When the latter were divided into subgroups on the basis of potential degree of contact among individuals, the distribution of these titers appeared to be related to the probable degee of personal contact among individuals in such groups. Among children convalescing from scarlet fever, the mean and range of these titers was elevated above the normal, as also among patients with rheumatic fever in a quiescent state of the disease. In active rheumatic carditis, however, the distribution of titers showed a higher mean and range than in the two clinical groups just mentioned. Of 23 cases thus far studied of clinical reactivation of rheumatic fever, all were accompanied by a rise in the streptococcal antihyaluronidase titer as measured turbidimetrically.

These distributions of titers among the clinical groups showed differences similar to those found by the mucin-clot-prevention test for streptococcal antihyaluronidase. The possibilities that the two tests measure the same or different antibodies are discussed in terms of titers observed in individual sera by the two tests and of the relationships between enzyme and substrate in each system.

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This study was supported by grants from the Life Insurance Medical Research Fund and the Helen Hay Whitney Foundation.

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