It has been demonstrated that perturbation of oxidative balance plays an important role in numerous pathological states as well as in physiological modifications leading to aging. In order to evaluate the role of the oxidative state in cells, biochemical and ultrastructural studies were carried out on K562 and HL-60 cell cultures. Particular attention was given to the transferrin receptor, which plays an important role in cellular iron metabolism. In order to evaluate if oxidative stress influences the transferrin receptor regulation process, the free-radical inducer menadione was used. The results obtained seem to indicate that oxidative stress is capable of inducing a rapid and specific down-modulation of the membrane transferrin receptor due to a block of receptor recycling on the cell surface, without affecting ligand-binding affinity. These effects were observed in the early stages of menadione treatment and before any typical signs of subcellular damage, including surface blebbing, a well-known cytopathological marker of menadione-induced injury. The mechanisms underlying such phenomena appear to be related to cytoskeletal protein thiol group oxidation as well as to the perturbation of calcium homeostasis, both induced by menadione. It is thus hypothesized that the data reported here represent a specific example of a general mechanism by which cell surface receptor expression and recycling can be influenced by oxidative balance.