Platelets respond to a wide variety of exogenous agonists that bind to distinct receptors on the platelet surface resulting in the intracellular generation of second messengers or the opening of ion channels, setting off a cascade of events leading to both physical and functional changes in the platelet. The cyclic nucleotides, cyclic adenosine 3′5′-monophosphate (CAMP) and cyclic guanosine 3′5′-monophosphate (cGMP) initiate a sequence of intracellular events that modulate many of these reactions in the platelet.