We studied serum acute phase reactant (APR) levels in 45 pediatric surgical patients. Alpha 1-acid glycoprotein (alpha 1-AG) showed a peak value on day 3 postoperatively (P.O.) and alpha 1-antitrypsin (alpha 1-AT) showed a high value on days 3-5 P.O. These glycoproteins returned to normal levels by day 21 P.O., but the level of haptoglobin (Hp) remained high until day 21 P.O. The postoperative changes of alpha 1-AG and alpha 1-AT correlated with the process of recovery from inflammatory conditions, but C-reactive protein (CRP) reached a peak on days 1-2 P.O. and returned to normal limits by day 14 P.O. In patients with infection, CRP returned to the normal level rapidly before recovery from infection. Of the 3 glycoproteins, alpha 1-AG seemed to be a valuable indicator of the pathological conditions. Postoperative changes in APR levels should be useful for early detection of postoperative complications. Persistent ileus led to an increase in APR levels, as a consequence of an inflammatory reaction due to breakdown of the intestinal mucosal barrier.