Apical membrane antigen 1 (AMA1) is an asexual blood-stage protein expressed in the invasive merozoite form of Plasmodia species, which are the causative agent of malaria. We have complemented the function of Plasmodium falciparum AMA1 (PfAMA1) with a divergent AMA1 transgene from Plasmodium chabaudi (PcAMA1). It was not possible to disrupt the PfAMA1 gene using 'knock-out' plasmids, although we demonstrate that the PfAMA1 gene can be targeted by homologous recombination. These experiments suggest that PfAMA1 is critical, perhaps essential, for blood-stage growth. Importantly, we showed that PcAMA1 expression in P. falciparum provides trans-species complementation to at least 35% of the function of endogenous PfAMA1 in human red cells. Furthermore, expression of this transgene in P. falciparum leads to more efficient invasion of murine erythrocytes. These results indicate an important role for AMA1 in the invasion of red blood cells (RBCs) across divergent Plasmodium species.