The importance of the colon for the absorption of calcium, fat, and fluid was studied in 118 patients with small-bowel resections of various lengths. The patients fell into two groups: 38 with ileostomy and 80 with part of or the whole colon in function. In patients with ileostomy, but not in patients with the colon preserved, the absorption of ⁴⁷Ca and fluid was inversely correlated to the length of the resected small intestine. In patients with extensive small-bowel resection (≤150 cm) the ⁴⁷Ca absorption was significantly higher when colon was preserved. In groups of equal small-bowel resections stool mass was significantly higher in patients with ilcostomy, but faecal fat was not. However, in both groups faecal fat was correlated to the length of the resected small bowel. The study shows that colon plays an important role for the absorption of calcium after small-intestinal resection and confirms the importance of colon for fluid absorption.