Purified human LDL (d=1.019 - 1.063 g/mL) is oxidized with copper (II) sulfate and labeled with DiI (1,1-dioctadecyl- 3,3,3,3-tetramethylindocarbocyanine perchlorate). The purified probe is ultrafiltered through a membrane and packaged aseptically under nitrogen. The product is provided in a solution with 154 mM NaCl and 0.34 mM EDTA, at pH 7.2.