Ardissino G, et al. - Eculizumab (ECU), a humanized antibody that blocks complement activity, has been successfully used in atypical hemolytic uremic syndrome (aHUS), but the best treatment schedule is not yet clear. In this current investigation, it was shown that a safe reduction in the frequency of ECU administration in aHUS, while keeping the disease in remission, was achievable via monitoring complement activity.