The clinical and laboratory data from 75 patients with altered vitamin B 12 absorption were reviewed. In 36 cases the diagnosis of pernicious anaemia had been established. Of these, 14 patients showed malabsorption of radiolabelled vitamin B 12, but the absorption of vitamin B 12 bound to the intrinsic factor (IF) was normal (Group A). The other 22 patients with pernicious anaemia showed altered free and IF-bound vitamin B 12 absorption (Group B). Laboratory and clinical data and the absorption tests (xylose and fat excretion) were more abnormal in group B than in group A. Finally, 39 patients (Group C) with general malabsorption showed alternation of the absorption of free and IF-bound vitamin B 12 (Group C). The clinical nd biological data were different in these patients from that found in groups A and B. It is possible that in patients with pernicious anaemia who are untreated an alteration of the intestinal mucosa may produce a malabsorption of vitamin B 12 even in the presence of intrinsic factor.