Black hairs that had been removed from a methamphetamine (MA) addict were treated with permanent wave, dye or decolorant liquids, and MA and amphetamine (AP) were quantified by a high-performance liquid chromatography/chemiluminescence detection method. The concentrations of MA and AP in the hair decreased significantly in all cases. Both MA and AP were stable in the permanent wave treatments, but not stable in the dye or decolorant treatments. As possible reasons for the decrease, the elution of MA and AP from hair in the permanent wave treatment, and the degradation of MA and AP in the dye or decolorant treatments might be considered. These results suggested that treatments of hair with permanent wave, dye or decolorant liquids interfered with determination of MA and AP in hair.