The effect of leavening of bread containing bran on the phytic acid content and on zinc absorption in man was studied. Twenty breads with leavening times varying from 0 to 120 h were prepared. The breads contained 250 g wheat bran/kg flour. The phytic acid content was determined after baking. The phytic acid content of bread containing bran was reduced to about 40% after 2 h of leavening and to 15% after 2 d. No further decrease was observed. Zn absorption from single meals was determined using a radioisotope technique. Forty-two students volunteered for these studies. They were served a breakfast of milk, butter, bread and 10, 16 or 30 g bran served either raw or baked into the bread with fermentation times of 15 min, 45 min, 3 h or 16 h. One meal contained no bran, but phytate and Zn were added in amounts equivalent to the content of 10 g bran. The amount and percentage of Zn absorbed increased at each bran level as fermentation was prolonged. The percentage of Zn absorbed was reduced by increased bran content in the meal. It is concluded that the fermentation of bread containing bran reduces the phytic acid content and increases Zn absorption from such bread. This may be of importance to people subjected to diets with a high cereal content, especially in combination with a low animal-protein intake.