Isolated rat hepatocytes containing 0.56-1.79 micrograms iron/10(6) cells and with an intracellular ATP concentration of 3-4 mM, accumulate iron from transferrin linearly with time for at least 3 h. At 37 degrees C the rate of uptake amounts to 0.3-0.7 pmol/mg cell protein per min. The uptake reaches a saturation level of 21-40 pmol/mg cell protein per h at 2.2 microM iron. At 5 degrees C the uptake does not increase over the time of incubation. Uptake of iron, but not binding of transferrin is increased 4-5-fold at oxygen concentrations 10-20 microM. At oxygen concentrations beyond these limits iron uptake is decreased. Iron taken up at low oxygen concentrations can be chelated by bathophenanthroline and bathophenanthroline disulphonate , but only if the chelators are present during the uptake experiments. The results suggest that iron uptake from transferrin by hepatocytes in suspension involves reductive removal of iron.