Electron-microscopical examination of the nucleus accumbens, caudate nucleus and frontal cortex was performed in 21 patients with Huntington's disease (HD) and 21 age-matched controls. In HD, nuclear membrane indentations (NMI) were found in 25%, 29% and 20%, respectively, of the neurons of these areas. In the control group these figures were 4%, 4% and 38%, respectively. Possible pathogenetic mechanisms of the NMI are discussed.