DL-Tryptophan (Standard) is the standard substance of DL-Tryptophan, and it is applicable for quantitative analysis, quality control, and related research in biochemical experiments. DL-Tryptophan ((±)-Tryptophan) containing dipeptides are interesting ingredients for functional foods as a natural prevention for hypertension with reduced side effects due to its selective inhibition of the C-domain. Low thalamic Tryptophan uptake appears to be a strong, independent predictor of long survival in patients with previous glioma treatment.