The complement system plays an important role in the physiopathology of acute myocardial infarction (AMI) taking part in myocardial damage and reperfusion injury. The aim of this study is to investigate the plasmatic levels of some complement components (C3c, C4 and C1-INH) during unstable angina (C1-INH) and their different concentrations in relation to the different myocardial areas affected by ischemia.The plasmatic levels of C1-INH, C3c and c4 in 30 patients affected by unstable angina, and those of 22 clinically healthy subjects (control group) were evaluated (Nefelometer Behering). The patients were divided into four groups according to the different myocardial area affected by ischemia (anterior, antero-lateral, lateral or inferior ischemia),No statistically significant differences were found in plasmatic levels of C3c, C4 and C1-INH between the group of patients and the control group. There is a statistically significant difference between the C1-INH levels of the patients with inferior ischemia and the plasmatic concentrations of the whole patients' group (p<0,01), the control group (p<0,01) and the group of patients with lateral ischemia (p<0,02).There seems to be a different activation of the complement system during unstable angina, in relation to the different myocardial area affected by ischemia.