Abstract: A competitive assay for the concentration of a cyclic nucleotide such as cyclic adenosine monophosphate combines, in a reaction chamber provided with a capture antibody, an antibody for the cAMP or other cyclic nucleotide, the sample to be assayed and a conjugate of cAMP and alkaline phosphatase. The mixture is incubated and washed, and after washing, a 1,2-dioxetane which is cause to decompose when contacted by the alkaline phosphatase of said conjugate is added. The light emission caused by decomposition is measured, with the strength of the signal being inversely related to the concentration of the cyclic nucleotide. Optionally, an enhancement agent in the form of a polymeric onium salt may be added, to further enhance the light emission.