Serum C-reactive protein rises in acute myocardial infarction, correlating positively with infarct size if thrombolytic treatment is not given. This correlation disappears if thrombolytic treatment is given, although the serum C-reactive protein concentration is still associated with the clinical outcome of the patient. We studied the effect of early coronary recanalization induced by thrombolytic treatment alone or combined with coronary angioplasty on the infarct related rise in serum C-reactive protein concentration. The C-reactive protein response caused by the myocardial infarct was lower in patients with an open infarct-related coronary artery than in patients with a closed infarct-related coronary artery, or in control patients who did not receive thrombolytic therapy. In control patients we found the expected strong positive correlation between infarct size and serum C-reactive protein (r = 0.58; P < 0.001, n = 48), which was similar to that in patients with a closed infarct-related coronary artery (r = 0.62; P < 0.001, n = 17). In patients with an open infarct-related coronary artery the correlation between infarct size and serum C-reactive protein was much weaker (r = 30; P < 0.01, n = 91). Consequently infarct size explained approximately 35% of the variation in serum C-reactive protein values in the control patients and 36% in the patients with a closed infarct-related coronary artery, but only 9% of the variation in the patients with an open infarct-related artery. Ejection fraction correlated negatively with serum C-reactive protein in both control and recanalized patients. The association was again much stronger in the control patients.(ABSTRACT TRUNCATED AT 250 WORDS)