The erythrocytes of the Colombian owl monkey Aotus trivirgatus griseimembra can be used for the long-term in vitro cultivation of Plasmodium falciparum employing a modified Trager-Jensen method. Cultures are grown in HEPES-buffered RPMI-1640 using a 4% suspension of monkey erythrocytes and 10% pooled heat-inactivated human AB serum, with initial parasitemias in a range between 0.2 and 0.5%. Adaptation of new strains from human erythrocyte cultures can be performed by simply subculturing from human to owl monkey erythrocytes in a stepwise manner. When 5% human AB serum is included in cultures to support growth, as much as 5% monkey serum can be added in order to investigate serum effects, such as antibody activity against P. falciparum. The Aotus trivirgatus continuous culture system has provided a stable, consistent source of infected erythrocytes for in vitro experimentation, and the techniques developed have been used to further refine and support the animal experiments in progress.