[en] Aqueous solutions of human HDL (high density lipoprotein) buffered at pH 7 (sodium phosphate 10^-2 mol.l^-1) and saturated with N₂0 or 0₂, have been irradiated with increasing doses between 0 and 800 Gy (dose rate 2.7 x 10^-2 Gy/s. The action of 0H^. or 0H^./0₂^.- free radicals generated by gamma radiolysis has been followed by several parameters: 1/ formation of thiobarbituric acid-reactive substances (TBARS), 2/ decrease of endogenous vitamin E, 3/ formation of conjugated dienes and 4/ appearance of a differential fluorescence. Initial irradiation yields of vitamin E decrease are of the same order of magnitude (∼10^-7 mol.J^-1) in N₂0 or 0₂ saturated solutions. Initial irradiation yields of TBARS formation are slightly different when the oxidation process is initiated by 0H^. free radicals (G(TBARS) = (0.26±0.02) x 10^-7 mol.J^-1) or by 0H^./0₂^.-free radicals (G(TBARS) = (0.5±0.05) x 10^-7 mol.J^-1). Moreover, according to the nature of the free radicals, important differences can be noticed, occurring whether irradiation doses are weak or high. These results are compared to those obtained with LDL (low density lipoproteins) in similar experimental conditions. 7 figs