Chrysamine-G (CG) is a carboxylic acid analogue of Congo red, a histologic dye which stains amyloid. CG binds to the beta-amyloid protein of Alzheimer's disease (AD) in vitro and partitions into the brain of normal mice. In this study, we demonstrate increased binding of [14C]CG to homogenates of several regions of AD brain as compared to control. The total binding of CG to AD brain was approximately two- to three-fold that of control brain. The cerebellum could be used as an internal standard for each brain as CG binding to cerebellum did not differ between AD and control. The binding of [14C]CG correlated with numbers of senile plaques and neurofibrillary tangles. In addition, CG could be used to stain cerebrovascular amyloid in tissue sections. These results suggest that CG may prove useful as an in vivo probe of amyloid deposition in AD.