At present, there are conflicting data regarding whether or not beta-carotene has a positive effect on iron absorption. This study was undertaken to evaluate possible interactions involved in the uptake of beta-carotene and iron in a human intestinal cell model (Caco-2). The Caco-2 cells were incubated with test solutions containing different amounts of ferrous chloride (10-50 microM) and beta-carotene (0.3-2.5 microM) incorporated in synthetic micelles. In the absence of iron, cellular accumulation of beta-carotene from synthetic micelles was proportional (r (2)=0.97, P <0.001) to the beta-carotene concentration in the test solution. However, with addition of ferrous chloride (30 microM), the beta-carotene uptake was significantly reduced (P <0.05), on average by 22%. There was also an inverse relationship between the beta-carotene uptake and iron concentration in the test solution (r (2)=0.93, P <0.05). Iron provided in physiological amounts inhibited the uptake of beta-carotene in the in vitro Caco-2 cell system.