An automated column-switching liquid chromatographic-electrospray ionization-mass spectrometric (LC-ESI-MS) method has been established for the determination of methamphetamine (MA) and its metabolites, amphetamine (AP), and p-hydroxymethamphetamine (p-OH-MA) in hair. The combination of an N-vinylacetamide-containing hydrophilic polymer online extraction column, an SCX semi-micro LC column, and an electrospray ionization interface provided the successful concentration, separations, and highly sensitive MS determinations of these analytes in a hair extract without tedious sample pretreatments. The limits of detection of these analytes were 0.02 ng/mg and 0.1-0.2 ng/mg in the selected-ion monitoring (SIM) and full-scan modes, respectively, when using a 100-microL hair extract sample that corresponds to a 2.5-mg sample of hair. The calibration curves using dibenzylamine as an internal standard were linear up to 30 ng/mg hair equivalents for all these analytes in the SIM mode. p-OH-MA, the detection of which in MA users' hair had not been previously reported, was detectable in all 22 hair specimens/sections from which 1 ng or more of MA was detected per milligram hair. The amount of p-OH-MA detected per milligram of hair is presented with those of MA and AP among the MA users population. The detection of AP and p-OH-MA, in addition to the parent drug MA with reasonable ratios, was found to be a useful indicator for distinguishing internal MA incorporation from external contamination.