The value of serial complement measurements for early diagnosis of sepsis, determination of septic complications and prognosis have been investigated on patients who were operated and patients with burns. The investigation was made at the Department of General Surgery, Faculty of Medicine, Cumhuriyet University on 63 patients. They were divided into two groups. Thirty-three patients with burns formed group A. Group B was formed by 30 operated patients. Both groups were classified as septic and nonseptic.In septic patients of both groups, C3c significantly decreased at the end of the first day (p <0.05) and insignificantly increased to admission levels at the 120th hour except septic patients in Group A (p>0.05). There were no statistically differentiations of C4 in this group.In conclusion, measurements of C3c provide guidelines for prognosis and adequacy of therapy; but serial complement measurement after the 24th hour seems to be even more valuable in the early diagnosis of sepsis. On the other hand, C4 determination is not necessary.