The effects of chronic methamphetamine administration (10 mg/kg, ip) on thiamine and its phosphate esters in the rat brain were studied. Thiamine triphosphate (TTP) decreased significantly in correlation to the stereotyped behavior. However, thiamine, thiamine monophosphate (TMP) and thiamine diphosphate (TDP) did not change significantly. In the chronic methamphetamine intoxicated rat, TMP and TDP decreased immediately after a single haloperidol injection (10 mg/kg, ip), and the level of TDP decreased significantly TTP in the brain, however, did not change for 60 minutes. Further studies on the relationship between biogenic amines and TTP which is supposed to be a neuroactive agent would be required.