C₉H₁₄O₃N₄, a dipeptide (/3-alanyl histidine), composed of the amino acids of /3-alanine and L-histidine. Discovered by G. S. Gulevich in 1900 in a meat extract. Molecular weight, 226. It crystallizes into colorless needles that are readily soluble in water but insoluble in alcohol. It is found in the skeletal musculature of most vertebrates.

Carnosine and its constituent amino acids are absent in certain species of fish (only L-histidine or /3-alanine is present); it does not occur in the muscle of invertebrates. The carnosine content in the muscle of vertebrates usually varies from 200 to 400 mg percent raw muscle weight, depending on the muscular structure and function; in the human body it ranges between 100 and 150 mg percent.

Carnosine has diverse effects on the biochemical processes that occur in skeletal muscles; however, its biological role has not been definitively established. The addition of carnosine to a solution bathing the muscle of the isolated neuromyal specimen causes restoration of contractions of the fatigued muscle.