Infection of the South American monkey “Sagui” (Callitrix jachus Linneu 1758) after inoculation with Plasmodium knowlesi have been observed. Intravenous massive inoculation brings death in about ten days. With intramuscular inoculation of smaller quantities of parasites, expontaneous cures has been verifies several times. The known 24 hours cycle as well as the morphological characteristics of the Plasmodium knowlsesi as observed in Rhesus infections, remains the same in the monkey studied. The vigor or Callitrix jacchus when kept in captivity is definitively less that observed with Rhesus monkeys, but as its buying cost is thirty times less, is could be considered a usefull new experimental animal for malaria research.