1. A protein component, fraction B, of lobster nerve extracts has been isolated and purified by differential ultracentrifugation and precipitation with zinc acetate.
2. Physicochemical data obtained from this protein and from fraction C are summarized.
3. Fraction B is present in lobster nerve extracts in higher concentration (relative to fraction A) than in blood.
4. A second component, fraction C, of sedimentation constant S20o = 13.2 has been isolated from lobster nerve extracts.