To investigate the role of the colon in increased oxalate absorption, we measured urinary oxalate and fecal fat excretion in 26 patients with gastrointestinal disease. Eight patients with steatorrhea of various causes (Crohn's disease [two], chronic pancreatitis [four], jejunoileal bypass [one] and extrahepatic biliary obstruction [one]) had hyperoxaluria (greater than 45 mg per 24 hours). All these patients had intact colons. In contrast, none of five patients with ileostomies and steatorrhea secondary to ileal resection had hyperoxaluria. Absorption of 14C-oxalate was increased in three patients with steatorrhea and intact colons but not in three patients with steatorrhea and an ileostomy. Thus, the colon is both the site of and required for increased oxalate absorption in enteric hyperoxaluria. The lack of a direct relation between fecal fat excretion and urinary oxalate excretion in the patients with hyperoxaluria and steatorrhea suggests that steatorrhea, although important, is not the only determinant in the pathogenesis of hyperoxaluria.