[en] [¹¹C]Methamphetamine ([¹¹C]MAP) was synthesized by an automated on-line [¹¹C]methylation system for positron emission tomography (PET) study. We newly produced a MAP sensitized dog by repeated MAP treatment and studied the brain distribution of [¹¹C]MAP in the normal and the MAP sensitized dog. The maximal level of accumulation of [¹¹C]MAP in the sensitized dog brain was 1.4 times higher than that in the control. No difference was found in the metabolism of MAP between the two conditions. The significant increase of [¹¹C]MAP in the MAP sensitized brain indicates that subchronic MAP administration causes some functional change in uptake site of MAP