Cu(II) mediated low density lipoprotein (LDL) oxidation has been followed by the changes in absorbance at 234 nm and the emitted low level chemiluminescence (CL). The similarity of the time profiles allows us to conclude that the emitted CL is due to the decomposition of a transient product, most likely a hydroperoxide. Red wine, as well as its fractions, afford a noticeable protection when added prior to the start of the LDL oxidation process. On the other hand, when they are added after the onset of the autocatalytic oxidation phase, red wine and its fractions behave as pro-oxidants. This is particularly evidenced by a strong burst of CL (enhancement of the light by a factor approximately 20). This burst is reduced by metal chelators (EDTA and DFO) and can be associated to a sequence of reactions such as XOH + Cu(II) --> X* + H(+) + Cu(I), Cu(I) + LOOH --> chemiluminescence where XOH is a phenolic compound and LOOH is a peroxide-like compound produced in the LDL oxidation.