In seven cases of Huntington's chorea, the ventrolateral thalamus was studied by quantitative cytometry. A selective 50 percent atrophy of microneurons (internuncial cells) was found while the macroneurons did not show significant atrophy. Thalamic microneurons might be presynaptic and postsynaptic inhibitory cells. Their specific atrophy in Huntington's chorea thus could be related to the known decrease of gamma aminobutyric acid (GABA) in Huntington's chorea.