Early and late brain distribution of iodine-labelled N,N,N'-trimethyl-N'-(2-hydroxy-3-methyl-5-iodobenzyl)-1,3-propanediamine (HIPDM) and iodine labelled N-isopropyl-p-iodoamphetamine (IMP) were compared in rat and one human patient with a recent stroke in the right middle cerebral artery area. In rat, an important 'redistribution' of cerebral activity was observed in various areas of the brain, mainly white matter, whereas no such observation was made with HIPDM. In the patient, the right area was hypoactive during the early SPECT with IMP and HIPDM, and redistribution was observed in the late SPECT only with IMP. We suggest that while HIPDM appears to reflect regional cerebral perfusion, IMP distribution is dependent upon metabolic brain activity.