['Heparin has anti-inflammatory properties. Serum tests after ERCP might serve as surrogate markers for inflammatory reactions. The aims were to study effects of low-dose unfractionated heparin on post-ERCP laboratory tests and on safety.', 'The design was prospective, randomized, double-blind, placebo-controlled. Eighty-nine patients were randomized to 5000 IE Heparin (0.2 ml of 25000 IE) or 0.2 ml 0.9% NaCL given s.c. 4h before and 4h and 18h after ERCP. Amylase, AST, ALT, CRP and leucocyte count were analyzed at these times and also after 48h. Adverse events were registered.', 'Significant increase was observed after 18h in the placebo group (n=44) for amylase (mean: 0.66 microkat/l, SD:0.8 vs. mean: 4.56 microkat/l, SD:9.9, p = 0.011), AST (mean: 1.37 microkat/l, SD: 1.5 vs. mean: l.96 microkat/l, SD:2.1, p = 0.049) and ALT (mean: 2.42 microkat/l, SD:2.7 vs. mean: 2.91, SD: 2.9% kat/l, p = 0.042). Corresponding elevations were not seen in the heparin group (n=41): p = 0.371, 0.395 and 0.25 respectively. Leucocyte count elevation was higher with longer duration in the placebo group. Mild pancreatitis occurred in 4.7% (placebo: 3, heparin: (1) and 4/89 (placebo: 2, heparin:(2) were excluded due to minor bleeding after the first injection.'] Is a preventive effect of unfractionated heparin on post-ERCP pancreatitis suggested by positive effects on laboratory markers?