Background: Immunoglobulin E (IgE) is important in allergic reactions and in host defense against parasites. IgE may also participate in the acute- phase response to physical stress. This study aimed to determine whether major abdominal surgery induced increased serum IgE levels, and whether treatment with ranitidine or prednisolone influenced the IgE response to surgery. Methods: For assessment of the IgE response to surgery and the effect of ranitidine, 24 patients scheduled for major abdominal surgery were randomized to receive either perioperative treatment with ranitidine or no treatment. To evaluate the effect of glucocorticoids, 24 patients undergoing major elective abdominal surgery were randomized to receive preoperative treatment with either prednisolone or placebo. IgE levels were determined in serum samples drawn pre- and postoperatively. Results: In the ranitidine study, both the control group and the ranitidine-treated group displayed a postoperative increase (P<0.001) of serum IgE. In the prednisolone study, a postoperative increase (P<0.05) of serum IgE was detected in the placebo group. No significant increase was found in the prednisolone-treated group. Conclusions: Major abdominal surgery induces an increase of serum IgE. This increase can be prevented by preoperative treatment with prednisolone, but not with ranitidine.