BACKGROUND:: To generate exhaustive data on the stability of human anti-immunotherapeutic antibodies. MATERIALS & METHODS:: Samples collected from over 100 different subjects at various timepoints were analyzed shortly after serum collection using specific ELISAs and re-analyzed after long-term storage or multiple cycles of freeze–thaw. The general acceptance criteria for incurred sample reanalysis for ligand-binding assays were applied, as well as alternative stricter acceptance criteria promoted by various white papers. RESULTS:: Anti-immunotherapeutic antibodies are stable in undiluted serum samples stored at -80°C for at least 3.5 years and 3–12 freeze–thaw cycles. CONCLUSION:: Samples were selected to cover the heterogeneity of the polyclonal human immune response, therefore this stability data can be extended to all anti-vaccine and anti-drug antibodies.