cAMP is a ubiquitous cellular second messenger that is a critical component of a signal transduction pathway linking membrane receptors and their ligands to the activation of internal cellular enzymatic activity and gene expression. cAMP is synthesized from ATP by membrane-bound adenylate cyclase and activates or inhibits various enzymes or cascade of enzymes by promoting their phosphorylation or dephosphorylation. Cayman's cAMP assay is a competitive ELISA that permits cAMP measurements within the standard curve range of 0.078-10 pmol/ml, typically with a sensitivity (80% B/B0) of 0.1 pmol/ml for acetylated cAMP. Non-acetylated cAMP has a range from 0.3-750 pmol/ml and a sensitivity (80% B/B0) of approximately 3 pmol/ml.