Novel blood-brain barrier permeant amyloid-targeting peptides and peptide conjugates are described. The peptide conjugates include a radioisotope or other label in a stable complex that translocates across brain capillary endothelial cell monolayers. The labeled peptide conjugate binds to amyloid plaques (Aβ) associated with Alzheimer's disease, and is useful for the targeted delivery of therapeutic and diagnostic molecules into the brain.