This study was designed to assess the circadian variation of the efficacy of thrombolytic therapy (TT) in 163 patients with acute myocardial infarction. Statistical analysis of the results suggests the existence of circadian variation in the efficacy of thrombolytic therapy with marked early morning resistance and significantly better late daytime results. There is a strong relationship between the normal physiologic rhythms of biochemical, hemodynamic, and hematologic parameters, observed in patients with CAD and the circadian fluctuations of efficacy of TT. Obviously the efficacy of TT is influenced by more evident impact of chronorisk factors during the early morning hours.