GC-MS of tissue extracts obtained from a parkinsonian patient who died from secondary causes during memantine (1-amino-3.5-dimethyladamantane) treatment showed the drug to be largely unmetabolized. In the kidney and liver a second peak corresponded to less than 1% of the main temporal lobe, hypothalamus and pons. Thus treatment with 2 X 10 mg memantine/day reveals an accumulation of the drug in microM concentrations in the brain. This is probably high enough to explain the ameliorating effect of memantine treatment in patients suffering from Parkinson's disease.