The role of l23I-N-isopropyl-p-iodoamphetamine (123I-IMP), a new agent used in brain imaging with single-photon emission computed tomography (SPECT), has been assessed in the early diagnosis of acute infarctive stroke and Alzheimer's disease (AD). The diagnosis of these conditions in their early stages has remained problematic, principally due to limitations of existing technologies. To more formally assess this new technology, we estimated the sensitivity and specificity of123I-IMP SPECT scanning in the diagnosis of stroke and AD. We based our assessment on a review of all published studies that reported on123I-IMP SPECT scans and which included three or more patients. The results from three major studies indicate that123I-IMP SPECT scanning has a higher sensitivity (92% to 100%) than computerized tomography (55% to 86%) in the early diagnosis of acute cerebral infarction. Preliminary findings from studies using123I-IMP SPECT in the diagnosis of early AD are promising and show a sensitivity of at least 69%. Furthermore,123I-IMP SPECT scanning clearly discriminates patients with advanced AD from normals: sensitivity has ranged from 50% to 100%, while specificity has ranged from 97% to 100%. Studies also suggest that it can discriminate AD patients from those with multi-infarct dementia. Our review indicates that123I-IMP SPECT may have an important future role in the early diagnosis and management of patients with acute infarctive stroke and AD.