Studies on vitamin B12 absorption were performed in three patients with total pancreatectomy, three with partial pancreatectomy and a single case of pernicious anemia by a whole body counting method. All three subjects with total pancreatectomy showed B12 malabsorption. In two out of the three patients, B12 absorption was improved by administration of pancreatic extract, pancreatin. Another patient showed the most improved absorption when normal human gastric juice in an amount of 20 ml was administered with pancreatin because of the lack of intrinsic factor in the gastric juice. The improvable effect of pancreatin on B12 absorption was markedly reduced by heating at 100°C for 10 min. The pancreatin, per se, had no intrinsic factor activity. Two patients with partial pancreatectomy showed normal or intermediate B12 absorption and a slight depression of B12 absorption by administration of pancreatin. The contamination by vitamin B12 in pancreatin might have been responsible for reduction of B12 absorption. The data obtained indicated that the normal secretory functions of both the pancreas and gastric intrinsic factor were necessary for an optimal B12 absorption. The possible mechanisms to account for the beneficial effects of pancreatin on vitamin B12 absorption are discussed.