Changes in the chemical structures of morphine and codeine in the presence of hydrogen peroxide, a major component of hair dye and decolorant treatments, were examined with high-performance liquid chromatography/mass spectrometry (LC/MS). A mixture of morphine and hydrogen peroxide solution, after incubation at 39 degrees C for 24 h, produced two reaction products (hydroxymorphines). When codeine was used in place of morphine, one reaction product (hydroxycodeine) was produced, in which the benzene ring was hydroxylated.