We studied the occurrence of the environmental radon daughters, 210Po (alpha particles), and 210Bi (beta particles), in the protein and lipid fractions of cortical gray and subcortical white matter from the frontal and temporal lobes of human brains of persons with Alzheimer disease (AD), persons with Parkinson disease (PD), smokers, or persons with no previous evidence of clinical neurologic disease (controls). We found a 10-fold increase in 210Po and 210Pb radioactivity in the protein fraction from both the cortical gray and subcortical white matter in AD and smokers, and a similar increase in the lipid fraction in PD. The pathognomonic distribution of the radon daughters to the lipids in PD and to the proteins in AD was inferred to reflect the increase of local chlorine availability to which radon daughters bound selectively. Cigarette smoking strongly increases radon daughter retention in the central nervous system.