Great reed warblers (Acrocephalus arundinaceus) are frequently parasitized by egg-mimetic common cuckoos (Cuculus canorus) in Hungary, and these hosts reject about a third of parasitic eggs. The timing of parasitism is important, in that the probability of rejection decreases with advancing breeding stages in this host. Also, egg rejection is more common when a clutch is parasitized by a single foreign egg, compared to parasitism by multiple eggs. We repeatedly parasitized great reed warbler clutches with moderately mi- metic foreign eggs, either with (1) one foreign egg (single parasitism) and, after 3 days, by all foreign eggs (multiple parasitism), or (2) all foreign eggs and, 3 days later, by only one foreign egg. Hosts ejected 26-53 % of the experimental parasitic eggs in the first stage of the repeated parasitism, but almost all eggs were accepted in the second stage, irrespective of whether the clutch was singly or multiply parasitized. Video-taping of the behavioural responses of hosts to exper- imental parasitism revealed no evidence for sensory con- straints on foreign-egg recognition, because hosts recognized and pecked the parasitic eggs as frequently in the secondstage of repeated parasitism, as they did in the first stage. We suggest that the relative timing of parasitism (laying vs. incu- bation stage), rather thanlearningto accept earlier-laid foreign eggs, results in higher acceptance rates of cuckoo eggs in repeated parasitism, because there is decreasing natural cuck- oo parasitism on this host species and, hence, less need for antiparasitic defences, with the advancing stages of breeding.