Sepsis with acute organ dysfunction (severe sepsis) is common and frequently fatal. Leptin, a hormone mainly generated by adipocytes, has Several activating effects towards T cells, monocytes, endothelium cells and cytokine production suggesting a protective role of leptin in the setting of an acute systemic inflammation serum leptin level on 2nd day can differentiate between sepsis and noninfectious SIRS and its level of 38.05µgm/L has a sensitivity of 93% and a specificity of 100% to diagnose sepsis.