Various catalytically active antibodies or abzymes have been detected recently in the sera of patients with several autoimmune pathologies, where their presence is most probably associated with autoimmunization. Normal humans are generally considered to have no abzymes, since no obvious immunizing factors are present. Recently we have shown that IgG (its Fab and F(ab)2 fragments) from the milk of normal humans possesses DNase activity. Here we demonstrate for the first time that the light chain of IgG catalyzes the reaction of DNA hydrolysis. These findings speak in favor of the generation of abzymes in the tissue of healthy mothers, and since a mother's breast milk protects her infant from infections until the immune system is developed, they raise the possibility that these abzymes may contribute to this protective role.