Binding of certain ligands or hormones to their specific G-protein couple receptors activates GTP binding proteins (Gs or Gi) which either stimulate or inhibit adenylate cyclase. cAMP activates or inhibits various enzymes or cascade of enzymes by promoting their phosphorylation or dephosphorylation. The cAMP signal is neutralized by hydrolysis of cAMP to AMP by phosphodiesterases. Therefore, the concentration of cAMP in a cell is a function of the ratio of the rate of synthesis from ATP by adenylate cyclase and its rate of breakdown to AMP by specific phosphodiesterases. The Cayman Chemical cAMP assay is a competitive EIA that exhibits a limit of quantification of 0.1 pmol/ml (at 80% B/B0) for acetylated cAMP. Non-acetylated cAMP can be assayed with an IC50 of approximately 20 pmol/ml and a detection limit of 3 pmol/ml.