The new generation of plasminogen activators promises certain advantages over the first-generation agents, particularly enhanced clot specificity. The tissue distribution, half-life, therapeutic profile, and optimum dosage, however, need to be evaluated for each chemically different agent. Whatever advantages these third-generation agents offer over the existing natural prototypes of the plasminogen activators will not be determined for some time. In addition, because an "agent of choice" has not been identified at this time, critical care nurses must understand the mechanisms of action of the various thrombolytic agents to ensure accurate and appropriate assessment, problem identification, and intervention in this era of reperfusion with thrombolytic therapy.