Experiments were conducted to determine effects of isolated lignin and intact lignin in foods on bioavailability of intrinsic iron in lignin-containing foods and of supplemental iron (FeSO4.H20). Standard curve and slope ratio methodology were employed to determine iron bioavailability to chicks. In one experiment, lignin content of foods ranged from 2 to 25% and iron bioavailability ranged from -20 to 140%, but no association between lignin content and bioavailability existed. In other experiments, increasing dietary lignin concentration from some natural sources reduced total iron availability, whereas increasing isolated lignin concentration had no effect. These results suggest that lignin structure or other unidentified factors determine intrinsic iron availability. No lignin source significantly decreased supplemental iron bioavailability.