Serum complement (C3, C4) levels in Libyan patients with acute myocardial infarction (AMI; 31 patients) and angina pectoris (AP; 11 patients) at the 1st day and 7th day of attack were estimated. A group of 26 healthy Libyans were taken as control subjects (CS). Serum C3 and C4 levels (mean +/- SD, mg/dl) were elevated at the 1st day in AMI as well as AP patients (C3 --> AMI1: 154.0 +/- 28.5, AP1: 152.0 +/- 45.0, CS: 132.0 +/- 8.0, ANOVA: p = 0.0072; C4 --> AMII1: 38 +/- 13, AP1: 37 +/- 17, CS: 29 +/- 6, ANOVA: p = 0.0160). No significant differences for the elevated C3 and C4 levels at the 1st day were observed between the two diseases groups (AMI1 vs AP1 --> C3: p = 0.879, C4: p = 0.818). At the 7th day, C3 and C4 levels were further elevated in AMI, while they remained at the similar elevated levels in AP (C3 --> AMI 7: 173.1 +/- 28.0, AP 7: 149.0 +/- 41.0, CS: 132.0 +/- 8.0, ANOVA: p = 0.0000; C4 --> AMI 7: 46.0 +/- 7.0, AP 7: 36.0 +/- 15.0, CS: 29.0 +/- 6.0, ANOVA: p = 0.0000). Again, no significance differences for the raised C3 and C4 levels at the 7th day was observed between AMI and AP patients (AMI 7 vs AP 7 --> C3: P = 0.059, C4: p = 0.06). The C3 elevation showed significant positive correlation in AMI group (r = 0.522, p = 0.003) while it was insignificant in AP patients (r = 0.037, p = 0.915). Regarding C4 levels, it was significantly correlated in AMI (r = 0.483, p = 0.006), and in AP, although it was positively correlated (r = 0.656, P = 0.028) the observed difference was not significant (t = 0.29, p = 0.778). In conclusion, serum C3 and C4 levels were more profoundly elevated in AMI compared to AP patients suggestive of an acute phase and inflammatory response.