This review by Daniel Otzen surveys how best to target α-synuclein — the aggregation-prone protein central to Parkinson's disease — with antibodies, weighing which molecular species and conformations to aim at for diagnostics and immunotherapy. It features Flow Induced Dispersion Analysis (FIDA) as a quantitative, in-solution method for characterizing antibody binding to α-synuclein, presenting FIDA data on the specificity of a nanobody (NB1) raised against α-synuclein oligomers and discussing how FIDA measures hydrodynamic radius, dissociation constants, fibril affinity and stoichiometry under native equilibrium conditions, even in complex patient samples. It is an example of using FIDA to quantify antibody–antigen binding affinity and specificity in solution.