Salicylic acid-d4 is intended for use as an internal standard for the quantification of salicylic acid by GC- or LC-MS. Salicylic acid is an active metabolite of the COX inhibitor aspirin and a plant hormone that has been found in Cucumis sativus.It protects Cucumis sativus leaves from infection by S. fuliginea or E. cichoracearum when used at a concentration of 10 mM, as well as inhibits A. thaliana root growth at 0.3 mM. Salicylic acid (1 and 4 mM) reduces IFN-γ- and TNF-α-induced increases in NOS2 expression in primary rat cardiac fibroblasts. It decreases urine prostaglandin E2 levels in dogs when administered at a dose of 40 mg/kg.