This paper presents, for the first time, repeated assessments of cerebral metabolism and neuropsychological competence in early Alzheimer's disease. Regional cerebral metabolic rates for glucose were measured with positron emission tomography and 18F-fluoro-2-deoxy-D-glucose on three occasions at 8-month intervals, in a 57-year-old man with Alzheimer's disease of 2 1/2 years' duration and with a family history of neuropathologically confirmed Alzheimer's disease. Data were compared with mean cerebral metabolic rates from 12 healthy men. No differences in regional cerebral metabolic rates for glucose were found on the initial patient scan, whereas metabolism on the second and third scans was reduced significantly in the parietal lobes and bilaterally in some parietal lobe regions. Memory loss was demonstrable at the first scan, but then and at later scans, other aspects of cognitive performance remained within normal limits (Wechsler Adult Intelligence Scale, Boston Naming Test, Two-dimensional Block Construction). The results show that memory loss can precede a measurable reduction of cerebral metabolism in early Alzheimer's disease, but that later reductions in parietal lobe metabolism may not be accompanied by additional measurable neuropsychological deficits.