Substance P is a bioactive 11-amino acid peptide (Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-amide) first isolated in 1931 from brain and intestine. The peptide is involved in many physiological processes including pain modulation, smooth muscle contraction, blood pressure control, kidney function and water homeostasis. Substance P is widely distributed in numerous tissues and body fluids including the central and peripheral nervous system, gastrointestinal tract, respiratory tract, visual system and circulatory system. Cayman"s Substance P ELISA is a competitive assay that provides accurate measurements of Substance P with a working range of 3.9 to 500 pg/ml, typically with an IC50 (50% B/B0) of ~30 pg/ml and IC80 (80% B/B0) of ~8 pg/ml. Inter- and intra-assay CV"s of less than 20% can be achieved at most concentrations of the standard curve. Due to cross-reactivity with Hemokinin-1, we do not recommend this ELISA to measure Substance P in serum and plasma samples.