Technical Abstract: Co-cultures of two human cell lines, Caco-2 and HT29-MTX mucus producing cells, have been incorporated into an in vitro digestion/cell culture model used to predict iron bioavailability. A range of different foods were subjected to in vitro digestion and iron bioavailability from digests was assessed with Caco-2, Caco-2 overlaid with porcine mucin, HT29-MTX, or co-cultures of Caco-2 and HT29-MTX at varying ratios. It was found that increasing the ratio of HT29-MTX cells decreased the amount of ferritin formed and resulted in an overall decline in the ability of the model to detect differences in iron bioavailability. At the physiologically realistic ratios of 90% Caco-2 / 10% HT29-MTX and 75% Caco-2 / 25% HT29-MTX, however, a mucus layer completely covered the cell monolayer and the in vitro digestion model was nearly as responsive to changes in sample iron bioavailability as pure Caco-2 cultures. The existing in vitro digestion/Caco-2 cell culture model correlates well with human iron bioavailability studies, but, as mucus appears to play a role in iron absorption, the addition of a physiologically realistic mucus layer and goblet-type cells to this model should give more accurate iron bioavailability predictions.