Rats were subjected to serial venesections 3 days prior to and then sequentially for 4 weeks after surgical removal of either the proximal or distal half of the small bowel. Total serum protein concentration and protein electrophoretic patterns were determined on these sera. Both sham-operated and unoperated animals served as controls. The data showed differences in serum proteins in the first week after operation between the three groups of operated rats and the unoperated controls. However, there were no significant differences in serum proteins between the sham-operated and the two types of resected animals. This indicates that the combined effects of laparotomy, anesthesia, pre- and postoperative fasting outweighed any additional early effects of loss of 50% small bowel on serum proteins. The study also demonstrates the necessity of having both unoperated and sham-operated control groups in designing experiments involving surgical extirpation of intestine.