Gangliosides and major membrane components were determined in caudate nucleus, putamen, and hippocampus of 12 cases with Alzheimer disease (AD) type I, also termed presenile or pure AD, and in age-matched controls. The concentration of gangliosides, a marker for axodendritic arborization, was reduced to 71% in caudate nucleus, 82% in putamen, and 66% in hippocampus of that in the controls. Significant diminution of total dry solids, protein, and phospholipids was also found in caudate nucleus and was most pronounced in hippocampus. The early signs of extrapyramidal features have been emphasized in AD type I. We now provide evidence that the neostriatum is affected in AD type I (the putamen, however, to a lesser extent than the caudate nucleus). The biochemical changes in these nuclei can be significantly related to scores of impairment of motor performance.