Empirical Formula (Hill Notation): C6H9N3O2, Molecular Weight: 155.15, cell culture tested, meets EP, USP testing specifications, from non-animal source, Synonym: (S)-2-Amino-3-(4-imidazolyl)propionic acid, NSC 137773. L-histidine has been used as a component in agar plates containing 5-fluorocytosine (5-FC) for the selection of yeast transformants. It has also been used as a component of adult mouse keratinocyte growth medium.