text: Norvaline is a non-proteinogenic unbranched-chain amino acid. It has previously been reported to be a natural component of an antifungal peptide of Bacillus subtilis. Norvaline and other modified unbranched chain amino acids have received attention because they appear to be incorporated in some recombinant proteins found in E. coli. Its biosynthesis has been examined. The incorporation of Nva into peptides reflects the imperfect selectivity of the associated aminoacyl-tRNA synthetase. In Miller–Urey experiments probing prebiotic synthesis of amino acids, norvaline, but also norleucine, are produced.