Sedimentation-coefficient measurements on human IgG, fibrinogen and α2-macroglobulin and pig thyroglobulin were made at rotor velocities of 15220–59780 rev./min and 25.0°C in capillary-type synthetic-boundary cells or ordinary cells. At the lowest velocity, IgG and fibrinogen gave results several per cent higher than at other velocities, whereas α2-macroglobulin and thyroglobulin gave values only about 1.5% higher. This behaviour of IgG and fibrinogen is attributed primarily to imperfect initial boundaries.
