Increased levels of lipid hydroperoxides (LOOH) are frequently associated with the oxidative mechanisms involved in physiological states as ageing and with serious pathological conditions. In the present work the physiological and the CCl4-induced lipid hydroperoxides levels in mice liver and kidney were determined. The analysis of LOOH tissue levels was performed through the oxidation of 1-napthyldiphenylphosphine (NDPP) into its oxide (ONDPP) and further quantification by high pressure liquid chromatography at 292 nm UV detection. The physiological level of lipid hydroperoxides levels was higher in the kidney (245 +/- 8 nmol LOOH/g of tissue) than in liver (164 +/- 5 nmol of LOOH/g tissue). After a single administration of CCl4 (0.25 ml/g) tissue LOOH reached a maximum level after 15 min (416 +/- 21 nmol/g kidney and 303 +/- 6 nmol/g liver) and then slowly decreased. LOOH levels in liver afforded an early indicator (15 min) of oxidative damage. LOOH levels in kidney remained significatively increased up to 60 min post administration. The described HPLC assay is a useful, simple and sensitive method to detect cellular oxidative stress and damage.