Kroth and coworkers recently described the preclinical comparison of [18F]AV1451 and [18F]RO948 with other fluoropyridine regioisomers.25 They found that different regioisomers gave rise to a remarkably diverse set of characteristics with regard to their binding affinity for AD and PSP tau, off-target binding to beta-amyloid and monoamine oxidases A or B as well as global brain uptake and washout in mice. The gene discussed is MAPT; the disease is Alzheimer disease.