['To find out if the severity of acute pancreatitis or the surgical treatment of severe acute pancreatitis influences HLA-DR and CD14 expression on peripheral blood monocytes.', 'Prospective open study.', 'University hospital, Austria.', '9 consecutive patients with severe acute pancreatitis in need of operative treatment, 5 patients with mild acute pancreatitis, and 7 healthy volunteers.', 'Samples of 5 ml blood were taken daily into endotoxin free tubes at same time points. Surgical treatment for severe acute pancreatitis consisted of blunt necrosectomy, operative lavage, laparostomy, and open drainage.', 'Correlation between HLA-DR and CD14 expression on peripheral blood monocytes on the one hand and the severity of acute pancreatitis and operative treatment of severe acute pancreatitis, on the other.', 'In patients with severe acute pancreatitis expression of HLA-DR and CD14 was significantly downregulated both before and after operation (p < 0.0001; ANOVA), compared with patients with mild acute pancreatitis or healthy controls. However the expression of the two cell surface markers was not affected either by the first operation, or by the reoperations.'] Does severe acute pancreatitis cause alterations in HLA-DR and CD14 expression on peripheral blood monocytes independently of surgical treatment?