BACKGROUND The effects of surgery on gastric emptying have been documented for a considerable time, but less is known about the effects in the small intestine. It is thought that there is minimal diminution in the absorptive capacity of the small intestine after operation, although there is no literature on drug absorption in the early period after surgery. This study investigated drug absorption from the small bowel in patients undergoing abdominal surgery. METHODS A prospective study of patients undergoing major abdominal surgery in which patients acted as their own preoperative controls was carried out. Patients were administered the test substances, acetaminophen and (99m)TcDTPA, before operation and 2 days after operation. Small intestine transit times, plasma concentrations and other pharmacokinetic variables were compared using Student's paired t-test. Two complementary studies were carried out to establish pharmacokinetic parameters. RESULTS There were no significant differences in the pre- and postoperative values of t(max), area under the curve, and area under the moment curve (AUMC) before and after operation (P>0.05). There were significant differences between the pre- and postoperative values of C(max) [C(max (preop))>C(max (postop)); P<0.05] and the pre- and postoperative values of mean residence time (MRT) [MRT((preop))<MRT((postop)); P<0.01]. CONCLUSIONS Drug absorption from the small bowel in the postoperative patient does not differ significantly from its preoperative absorptive capacity.