Microcomplement fixation analysis of albumin relationship shows that the Balearic green toad (Bufo viridis balearicus) is not an original, autochthonous member of the basically Miocene fauna of these western Mediterranean islands, but a quite recent newcomer. The plasma protein pattern clearly points to its close populational relationship to the Tyrrhenian islands' conspecifics. The male and female release vocalization shows the same, and this is in accordance with the external morphology too. There has been no possibility for toads to reach the Balearic Islands in Pleistocene or Holocene via land bridges, nor are they candidates for any sea drifting. Anthropogenic introduction must be assumed. This corresponds to its clear subfossil documentation beginning in the bronze age Talayot culture that shows connexions to the Sardinian one. Deliberate introduction for mythological reasons is discussed. The Balearic amphibian fauna has been greatly changed by human activities, to which can be attributed the existence ofthree of the four species actually living there. Studies on the origin of members of the herpetofauna in any Mediterranean island system or coastal region must pay more attention to this possibility in future.