Alzheimer's disease (AD) can currently be diagnosed conclusively only after death by observing the characteristic neurofibrillary tangles and plaques in brain sections. Methods that would allow the accurate detection of amyloid β-protein (Aβ) accumulation in the living brain of Alzheimer's patients early in the disease are needed to allow early pharmaceutical interventions that reduce Aβ formation and retard or even prevent the disease. Now, Wengenack et al. report on a promising technique for imaging A β in the living brain. They show that 125I-labeled Aβ crosses the blood–brain barrier (BBB) and labels brain Aβ deposits both in living mouse models and in human AD brain sections. Furthermore, they enhance the radiolabel's ability to cross the BBB by linking it to the polyamine putrescine (see pp. 868 and 825).