To develop a method of detecting methadone in the human brain by immunohistochemistry, brain tissue of frontal cortex, cerebellum, hippocampus, basal ganglions and brain stem from victims of a lethal methadone overdose was examined. The staining was performed with a monoclonal anti-methadone antibody from the mouse, originally developed for immunochemichal purposes (ELISA). With the help of the DAKO((R)) Catalyzed Signal Amplification (CSA) System, a specific positive immunoreaction was obtained in the neurons of the frontal cortex and hippocampus, as compared with specimen from deaths without exposition to methadone. Thus, along with metamphetamine, phenobarbital, morphine and insulin, immunohistochemical detection is also possible for methadone and the intake of this medicament can now be proven morphologically.