This is a colorimetric competitive immunoassay kit for the quantitative determination of extracellular cAMP diluted in buffer or intracellular cAMP in cells or tissues lysed in 0.1 M HCl. 0.1M HCl is used to stop endogenous phosphodiesterase activity and stabilize the released cyclic AMP. The 0.1M HCl treated samples are then analyzed directly in a microtiter plate without extraction, drying and reconstitution.