Activation of intracellular signaling pathways in circulating leukocytes represents an early step in systemic immune-inflammatory response occurring e.g. in acute pancreatitis (AP) and sepsis. Previously, we found aberrations in the phosphorylation of leukocyte signaling proteins in patients with sepsis or AP (measured <48 h from hospital admission) resembling each other and associating with AP severity. Of these patients, those with sepsis or severe AP complicated by persistent organ dysfunction (OD+, = 17) and patients with moderately severe AP (OD-, = 6) were followed up in this study by measuring the phosphorylations at two additional time points (2-4 and 5-8 days after the initial sample) using phosphospecific whole blood flow cytometry. Twenty-eighty healthy subjects served as controls (HC). Constitutive STAT3 phosphorylation (pSTAT3) declined in monocytes and neutrophils of OD-/OD + and in lymphocytes of OD + and remained higher in OD- than HC. Monocytes of OD-/OD + showed low pSTAT3 and pSTAT1 levels in response to IL-6 through follow-up. Monocyte pNF-κB levels in response to TNF, LPS and in OD+, to in OD-, and lymphocyte pNF-κB levels in response to TNF in OD- increased during follow-up but remained lower than in HC, and neutrophil pNF-κB levels in response to TNF declined in OD-. Phorbol myristate acetate + Ca ionophore-stimulated pERK1/2 decreased in neutrophils of OD-/OD+. To conclude, in patients with moderately severe or severe AP or sepsis, improvement and molecular events contributing to OD can be assessed at the level of blood leukocyte signaling.