Lipase activity, bile salt concentration and intraluminal phase of lipid resorption are investigated in 4 different regions of the dog small intestine. Lipase activity remains constant throughout the first half of the small intestine but drops to low values in the distal small gut. Conjugated bile salts concentration rises progressively from the duodenum until the upper limit of the distal quarter of the small bowel is reached, where it commences to drop until zero is reached at the end of the small bowel. In the duodenum the low pH (