Aggressive encounters were staged between two species of Puerto Rican lizards (Anolis cooki and Anolis cristatellus) which share the same microhabitat (syntopic). The intensity of these interspecific matches was as great as their respective conspecific matches. When the two species interacted with either “look alike” congeners (A. cooki with A. monensis and A. cristatellus with A. gundlachi) or with the quite different appearing A. evermanni, aggressive intensity was only 1/6 that of the cooki-cristatellus encounters. It seems that A. cooki and A. cristatellus recognize each other as competitors; it was improbable that this interspecific aggression was caused by the two species misidentifying each other as conspecifics. Because A. cristatellus eventually dominated A. cooki during staged encounters, it is predicted A. cristatellus should ecologically displace A. cooki in their syntopic zones of contact.