Infections that cause the Gombak and Smithsonian strains of Plasmodium cynomolgi were induced in Macaca mulatta, Aotus lemurinus griseimembra, Aotus nancymai, and Saimiri boliviensis monkeys. Transmission of the Gombak strain to Aotus spp. monkeys was obtained by the injection of sporozoites dissected from the salivary glands of experimentally infected Anopheles dirus and by the bites of infected An. dirus and Anopheles farauti mosquitoes. Two S. boliviensis monkeys were infected via the injection of sporozoites dissected from An. dirus. Prepatent periods in New World monkeys ranged from 14 to 44 days, with a median of 18 days. The Smithsonian strain was transmitted via sporozoites to 1 A. lemurinus griseimembra and 9 A. nancymai monkeys. Prepatent periods ranged from 12 to 31 days.