The second component of complement (C2) as an index of hereditary angioneurotic edema.

Measurements of C2 hemolytic activity were performed in the sera of 13 patients with Hereditary Angioneurotic Edema. Prior to treatment, C2 values correlated with the severity of the disease in each patient. During androgen therapy with Danazol, C2 measurements reflected the clinical benefit of the drug more accurately than C4 levels, thus explaining the effectiveness of low drug doses. This study also suggests that breakdown products of C2 may play an essential role in the pathogenesis of the edema.