The aim of this investigation was to elucidate a possible correlation between lipid peroxidation, antioxidant concentrations and erythrocyte membrane fluidity in plasma from newborns. Ten healthy newborns were recruited. Venous blood samples were collected at birth, and thereafter at 3 and 72 h postnatal age. The following parameters were assessed: hydroperoxides, Coenzyme Q10 and alpha-tocopherol both in plasma and in erythrocyte membranes, and fluorescence polarization (as a tool for assessing membrane fluidity). Hydroperoxides were shown to be high in erythrocyte membranes at birth and significantly decreased at 3 and 72 h after birth. In the erythrocyte membranes, coenzyme Q10 content showed an opposite behaviour with respect to the plasma compartment. Membrane fluidity appeared unchanged even in the presence of the above mentioned modifications.