AIM: To unravel the differences between systematic inflammatory response syndrome (SIRS) of acute pancreatitis compared to the same syndrome in sepsis.METHODS: Twenty-five patients were enrolled, 12 with sepsis and 13 acute pancreatitis. After diagnosis 20 mL blood was sampled. Half were assayed for isolation of monocytes and 10 mL was centrifuged for serum test of tumor necrosis factor alpha (TNFα) and interleukin-6(IL-6). Half of monocytes were incubated in the presence of patients' serum and supernatants were collected. The other half was treated for estimation of optical photometry under caspase-3 inhibition. TNFα and IL-6 were estimated by an enzyme immunoassay.RESULTS: median ± SE of serum IL-6 in septic patients and acute pancreatitis patients was 192.30 ± 35.40 ng/L and 21.00 ± 16.05 ng/L, respectively (P ＜ 0.01). Respective values of caspase-3 were 0.94 ± 0.17 pmol/min 104 cells and 0.34 ± 0.09 pmol/min 104 cells (P ＜ 0.05).IL-6 of monocyte supernatants of patients with sepsis was significantly increased after addition of patients' serum, while that of patients with acute pancreatitis did not show significant difference.CONCLUSION: The data have shown that monocyte activity is different between acute pancreatitis and sepsis. This phenomenon might be explained as a different pathway to the pro-inflammatory cytokines release or could be a novel anti-inflammatory response in acute pancreatitis.