Ultrastructural study of the nucleus accumbens, caudate nucleus and frontal cortex of patients with Huntington's disease showed that neuronal nuclear membrane indentations were significantly more frequently present in the nucleus accumbens and caudate nucleus, than in a control group. The astrocyte/neuron ratios in the same areas were also found to be higher in the Huntington patients. In a search to find out whether this finding is unique in Huntington's disease the brains of patients with several other diseases of the central nervous system, characterized by involuntary movements and/or dementia (Pick's disease, Down's syndrome, Alzheimer's disease, Parkinson's disease, Creutzfeldt-Jakob disease, tardive dyskinesia and multi-infarct dementia) were investigated in the same way. Although some findings were similar in this group, the Huntingtonian brains could be almost completely separated, with the exception of one patient with Creutzfeldt-Jakob disease, by the use of a discriminant analysis, taking into account the percentage of neurons with nuclear membrane indentation and astrocyte/neuron ratio of three areas of grey matter.