Abstract The effect of oxidative stress in vitro induced by radical generating systems (RGS) (Fe 2+-EDTA and Fe 2+-EDTA plus H 2O 2) on synaptosomal and microsomal ion transport systems as well as on the membrane fluidity was investigated. Oxidative insult reduced Na +, K +-ATPase activity by 50.7 % and Na +-dependent Ca 2+ uptake measured in choline media by 46.7%. Membrane fluidity was also significantly reduced as observed with the fluorescent probe. Stobadine (ST) prevented the decrease in membrane fluidity and Na +-dependent Ca 2+ uptake, however Na +, K +-ATPase activity was only partially protected, indicating a more complex mechanism of inhibition. Incubation of microsomes with RGS led to the loss of ability of membranes to sequester Ca 2+, as well as to the decrease of Ca 2+-ATPase activity and to the increase of Ca 2+permeability to 125.1%. The relative potency of the two RGS to decrease membrane fluidity correlated well with the system's potencies to induce lipid peroxidation. The extent of protection against depression of Ca 2+uptake values and Ca 2+-ATPase activity by membrane soluble antioxidants (U-74500A, U-83836E, t-butylated hydroxytoluene-BHT and ST) was dependent on the experimental conditions and on the dose and nature of antioxidant used. ST seems to be at least as affective as BHT and 21-aminosteroids, and more potent than tocopherol acetate. Water soluble glutathione had no significant effect on the RGS induced inhibition of Ca 2+-ATPase activity. Combination of ST with glutathione enhanced ST antioxidant efficacy, so drug combination might be beneficial therapeutically.