This work briefly describes available sensors for cAMP and cGMP. Many sensors are based on derivatization of naturally occurring products such as immunoglobulins, protein kinases, etc. Only a few published works deal with chemosensors, which are built up by "total" chemical synthesis. This field stays opened for combinatorial chemist. The best sensors are protein kinases genetically modified with mutants of green fluorescent protein, which allow screening of entire cell cultures.