A strain of yellow fever virus of jungle origin was easily maintained by alternate passage through a species of marmoset (Callithrix aurita) and Aedes aegypti mosquitoes. Nine cycles have been completed.
Yellow fever virus, also of jungle origin, was similarly passed through cebus monkeys (Cebus versutus) and Aedes aegypti. Five cycles were completed when the series was voluntarily interrupted.
Using Haemagogus equinus as vector in conjunction with the marmoset as host, three cycles were completed before the series was interrupted for lack of fresh mosquitoes.
The implication of these observations in relation to the epidemiology of South American jungle yellow fever is briefly discussed.