Rabbit red blood cells (RBC) were exposed in vitro to an oxygen-radical-generating system represented by iron and ascorbic acid. Under these experimental conditions we have investigated the effect of this system on some intracellular rabbit reticulocyte and erythrocyte enzymes. The results obtained have shown a pronounced decay of hexokinase activity both in the erythrocytes and reticulocytes when exposed to these radical species. We have found that the amount of hexokinase inactivated is at least three times higher in a blood sample with a percentage of reticulocytes of 50-60%. This different behaviour of the hexokinase decay in the erythrocytes and reticulocytes could be due to its different intracellular distribution related to the two distinct cells. In addition we have evaluated some important intracellular compounds involved in maintaining the redox and the energetic state of the cell such as the reduced glutathione and the adenine nucleotides and their degradation products, in order to understand if there is any correlation between the hexokinase decay and a change concerning the metabolic conditions of the rabbit reticulocytes and erythrocytes exposed to free radicals.