BACKGROUNDPositron emission tomography (PET) and single photon emission computed tomography (SPECT) are imaging modalities that can be used for in vivo evaluation of brain function in health and in disease. This review focuses on research into the underlying neurobiology of Alzheimer's disease (AD) using these modalities between 1995 and 1998. By binding radioactive molecules to water, neurotransmitters, or products of intermediary metabolism and imaging the distribution of radioactivity within the brain, PET and SPECT images can provide information on neural/synaptic function, the status of neurotransmitter systems, or specific metabolic processes within the brain under controlled conditions.REVIEW SUMMARYPET studies during the review period evaluated a wide range of metabolic, neurotransmitter, and genetic abnormalities thought to be involved in the etiology and pathogenesis of AD and AD‐associated cognitive symptoms. Several large SPECT studies measured the sensitivity and specificity of imaging as part of the evaluation of dementia. Few studies evaluated management of AD.CONCLUSIONSRecent PET and SPECT research focused primarily on 1) identifying the important neuropathological processes underlying AD or AD symptoms in vivo and 2) finding a biological marker for preclinical diagnosis. This knowledge is essential for developing and testing novel therapies to enhance AD therapy.(THE NEUROLOGIST 6:28‐43, 2000)