Previous observations have shown that individuals migrating from a malaria free area to a malaria endemic region in North Eastern Irian Jaya quickly acquire anti-parasite immunity, in an age-dependent manner. Sera from migrants and long-term residents in this area were examined for their ability to agglutinate a range of Plasmodium falciparum isolates and to disrupt erythrocyte rosettes. Antibody responses to merozoite surface protein 2 (MSP2) and ring-infected erythrocyte surface antigen (RESA) were also determined. The range of isolates agglutinated by sera from the migrants approached that seen in long-term residents. No difference was found between migrant adults and children in the range of agglutinating antibody, size of agglutinates, nor disruption of rosettes. Anti-MSP2 and anti-RESA antibodies were the only factors examined which showed a correlation with age. We conclude that although antibody to parasite neoantigens expressed on the surface of infected erythrocytes may play a role in the acquisition of immunity, the humoral response to other P. falciparum antigens is more likely to account for the age-dependent prevalence of parasitaemia observed.