[1] Kynurenine and its further breakdown products carry out diverse biological functions, including dilating blood vessels during inflammation[2] and regulating the immune response.

[4] Kynurenine is present in the lens and retina as one of multiple tryptophan derivatives produced in the eye, including 3-hydroxykynurenine, that together provide UV protection and aid in enhancing visual acuity.

[5][6] The use of kynurenine as a UV filter is consistent with its photostability and low photosensitization, owing to its efficient relaxation from the UV-induced excited state.

[23] Kynurenine has also been identified as one of two compounds that makes up the pigment that gives the goldenrod crab spider its yellow color.

[20][33][34][35][36] It is hypothesized that the kynurenine pathway is partly responsible for the therapeutic effect of lithium on bipolar disorder.