Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the ongoing COVID-19 pandemic. It is responsible for more than 1 million deaths worldwide already [1]. Because preventive and anti-viral treatment options are still limited, COVID-19 convalescent plasma (CPP) has been suggested as a potential therapy [2–4].

‘Convalescent’implies that anti-SARS-CoV-2 antibodies are present in plasma collected from individuals recovered from COVID-19. However, the dose and nature of antibodies required to effectively interfere with a SARS-CoV-2 infection is unclear. Most ongoing observational studies and prospective clinical trials currently focus on neutralizing antibodies (nAbs) that interfere with viral binding to host cells, but non-neutralizing antibodies might mediate a therapeutic effect as well. These and other unknowns highlight the importance of testing CCP efficacy in randomized trials. This commentary consequently does not claim to provide evidence on how to select potent CCP, but does want to provide an opinionbased discussion on how to investigate CCP potency. The antibody level in CCP varies greatly between donors. Therefore, it is required to measure antibody titer and/or to assess the neutralization potency of CCP. The current gold standard for the latter is in vitro viral neutralization like in the plaque reduction neutralization test (PRNT) or microneutralization (MN) assay. Both measure the ability of nAbs to prevent infection in vitro calculated either as a reduction in the formation of plaques or as the inhibition of viral infectivity in a cell monolayer,