Nine samples of Plasmodium falciparum were collected from migrant workers who were infected in the State of Rondônia, Brazil. These samples were maintained in culture for characterization by enzyme typing using acetate cellulose electrophoresis, drug susceptibility to chlo-roquine, amodiaquine, mefloquine and quinine and antigenic diversity analysis using strain specific monoclonal antibodies. The results obtained have confirmed major variation among all samples studied: it was found consistent resistance to chloroquine moderated resistance to amodiaquine and quinine and susceptibility to low levels of mefloquine; only two isolates have shown susceptibility to all drugs in the in vitra assays. Enzyme typing showed presence of both GPI 1 and 2 and ADA 1 and 2 parasites, while for PEP and LDH all samples were type 1. Se-rotyping with PSA monoclonal antibodies showed presence of three different serotypes (II, III and IV). These results confirm: a) variation among samples for markers analysed; b) in this area and for the small number of samples studied, no significant differences or new types of parasites were seen.