Results from methanolysis of Bence Jones JJO protein followed by dinitrophenylation allowed us to identify seven DNP derivatives, one of them showing a clearly more intensive colour corresponding to di-DNP-tyrosine. These data indicated that protein JJO should not present PCA as an N-terminal residue. The knowledge that N-terminal tyrosine is a characteristic residue of V λ III domains allowed us to tentatively assign the BJP (JJO) variable region as a member of the V λ III sub type. Through Ouchterlony analysis Bence Jones (JJO) protein gives a spur over another λ protein (BJP Mau) using as reagent rabbit antiserum to BJP (JJO). These data could lead to a preliminary but inconclusive speculation that BJP (JJO) is associated with antigenic sub type St-III+ as described for other V λ III sub types.153121122