Serum beta-galactosidase activity was found to be markedly increased in clotting blood from normal subjects, but patients with galactosialidosis showed only a slight increase of this enzyme activity. Consequently, the beta-galactosidase activity was low in serum after long-term clotting in patients with this disease. The mechanism of the enzyme activation is unknown. The use of anticoagulants completely inhibited the activation.