The leading pathophysiological changes during sepsis include systemic abnormalities in the immune response. Due to the general character of these disturbances, sepsis is usually studied as a homogenous clinical condition. We aimed to compare the immune response in intraabdominal sepsis (IAS) and pneumonia-derived sepsis (PDS). The following cell populations were examined: white blood cell count (WBC), monocytes, lymphocytes:CD3⁺, CD4⁺ and CD8⁺ T cells, B cells, and NK cells. In both studied groups (i.e. IAS and PDS), the WBC was elevated. However, it was significantly higher in the IAS group than in the PDS group. The difference was due to a lower granulocyte count, as well as a lower monocyte count in PDS. We found no significant correlation between the total lymphocyte number and CD3⁺CD8⁺ T cells in either form of sepsis. Similarly, we observed no correlation between the total lymphocyte number and the NK cells subset in IAS. However, the numbers of CD3⁺CD8⁺ and NK cells correlated similarly in both types of sepsis. Both studied types of sepsis induced profound lymphocytopenia, with marked loss of CD8⁺ T cells and the NK cells. However, the similarrelation between them, which was independent of the infection type, suggests that the NK and CD3⁺CD8⁺ cellshave shared mechanisms of regulation. The primary site of infection has an impact on the global immune reaction. These alternations include especially myeloid cells: granulocytes and monocytes which disappear from peripheral blood during PDS, but increase in IAS.