There exists strong evidence that tumor growth can be actively controlled by the host immune system and interleukins are known to play a significant role in immune response regulation. Inflammatory cytokines play important roles in the pathogenesis of lymphomas. This study was conducted to investigate the serum levels of IL-6 and IL-10 in patients with aggressive non-Hodgkin's lymphoma (A-NHL) and the relationships with prognostic parameters and therapy. These serum factors were measured in 46 A-NHL patients pathologically verified before and after chemotherapy in comparison with 21 healthy controls using enzyme-linked immunosorbent assays (ELISAs). There were significant differences in the serum IL-10 and IL-6 levels between A-NHL patients and controls (p=0,038 and p<0,001, respectively). None of the prognostic parameters analyzed was significantly correlated with the serum IL-6 concentrations. This was also true for serum IL-10 values, except for LDH and bone marrow involvement. Serum IL-10 levels were elevated in the group of patients with high level LDH compared with the group of patients with a normal level (p=0,017). Also, serum IL-10 levels were significantly different in the presence or absence of bone marrow involvement (p= 0,016). In addition, we found a significant relationship between the serum levels of serum levels of IL-6 and IL-10 in patients with A-NHL (r=0,47, p<0,001). We found that serum IL-10 levels decreased due to chemotherapy effect independent of the chemotherapy response (p= 0,027). However, serum IL-6 levels were not changed. In conclusion, our data suggest that higher serum IL-6 and IL-10 levels can be useful for diagnosis of A-NHL. However, our sample size is small, and larger scale research is needed in this field to provide new knowledge.