Extensive mobilization of the duodenum is essential in the performance of the Billroth I procedure. Should there be a marked inflammatory reaction, especially in the region of the common duct, a more conservative procedure, such as a pyloroplasty or gastroenterostomy and vagotomy, should be considered. If it appears that the duodenum, especially in the region of the ulcer, can be well mobilized, the peritoneum is incised along the lateral border of the duodenum and the Kocher maneuver is carried out. Usually it is unnecessary to ligate any bleeding points in this peritoneal reflection. With blunt finger and gauze dissection the peritoneum can be swept away from the duodenal surface as the duodenum is grasped in the left hand and reflected medially (Figure 2). It is important to remember that the middle colic vessels tend to course over the second part of the duodenum and are many times encountered rather suddenly and unexpectedly. For this reason the hepatic flexure of the colon should be directed downward and medially and the middle colic vessels identified early (Figure 2). As the posterior wall of the duodenum and head of the pancreas are exposed, the inferior vena cava readily comes into view. The firm, white, avascular ligamentous attachments between the second and third parts of the duodenum and the posterior parietal wall are divided with curved scissors, down through and almost including the region of the ligament of Treitz (Figure 2). This extensive mobilization is carried downward in order to ensure a very thorough mobilization of the duodenum. Following this, the omentum is separated from the colon, as described in Plate 27. In obese patients it is usually much easier to start the mobilization by dividing the attachment between the splenic flexure of the colon and the parietes (Figure 3). An incision is made along the superior surface of the splenic flexure of the colon as the next step in freeing up the omentum. This should be done in an avascular cleavage plane. The lesser sac is entered from the left side. Care should be taken not to apply undue traction upon the tissues extending up to the spleen, since the splenic capsule may be torn, and troublesome bleeding, even to the point of requiring splenectomy, may be encountered. The omentum is then dissected free throughout the course of the transverse colon.