[11C]PIB and [18F]FDDNP were examined on five aged and five young adult male rhesus macaques using positron emission tomography. Both tracers showed increased accumulation in the striatum, thalamus, cingulate and pons in the aged group. Compared to [11C]PIB, [18F]FDDNP showed higher accumulation in the cortical regions of aged animals as well as young animals. Although [18F]FDDNP may have possible usefulness for imaging, including other proteins, [11C]PIB may be better for amyloid imaging owing to lower non-specific binding.