L-Asparagine-d3 is intended for use as an internal standard for the quantification of L-asparagine by GC- or LC-MS. L-Asparagine is a non-essential amino acid. It is formed from L-aspartic acid and L-glutamine by asparagine synthetase (ASNS), and it is deamidated by L-asparaginase to produce L-aspartic acid and ammonia. L-Asparagine (0.3 mM) reverses ASNS siRNA knockdown-induced decreases in proliferation in a panel of six human cancer cell lines, indicating that both exogenous and endogenous L-asparagine promote proliferation of these cells. Formulations containing L-asparagine have been used as dietary supplements.