Cod, haddock, salmon, herring, skate and lobster, were investigated, the first two alone proving to be closely related chemically. In the first four the total non-protein nitrogen is of the same order; but in skate it is [Formula: see text] times as great, due to urea, ammonia and other volatile bases, and in lobster [Formula: see text] times as great, due to the monoamino acid and histidine-arginine fractions. Cod is very rich in the lysine fraction and poor in the histidine-arginine fraction, the reverse of the condition in ox. In herring this difference is also present but is not so great. In lobster the lysine fraction is slightly less than in cod but the nitrogen of the histidine-arginine fraction is extremely high.