1.Three hundred and sixteen neotropical rodents, belonging to twenty different species, were tested against several strains of yellow fever virus.
2.Coendou prehensilis, C. paraguayensis, Dasyprocta aguti, D. aguti maraxica, D. azarae aurea, Akodon arviculoides and Sylvilagus brasiliensis were found to be resistant to all strains of virus used. None circulated virus and, in general, the immunity response was poor.
3.Among the rodents belonging to the genera of Cercomys, Euryzygomatomys, Cavia, Nectomys and Oxymycterus only a small percentage circulated traces of virus.
4.Of the three species of Proëchimys tested, one, P. cayennensis roberti, was found to be resistant to the virus. Individuals of P. iheringi circulated virus, in traces, after the inoculation of the Asibi strain but were resistant to two jungle strains (J.Z. and O.C.). However, rodents belonging to the species P. dimidiatus circulated virus when infected with any one of these three strains. In general circulating virus was present only in small amounts and persisted for only 1 or 2 days in the blood stream. However, occasional individuals circulated virus for longer periods.
5.Of the three species of Oryzomys tested, one (O. laticeps) circulated more virus than the other two (Oryzomys sp. and O. intermedius), both of which showed only traces of virus in the blood stream after inoculation.
6.Sciurus ingrami was found to circulate virus after inoculation with the Asibi and the J. Z. strains, but not after inoculation with the O. C. strain. However, all the animals inoculated with the O. C. strain developed antibodies.
7.Cuniculus paca was the only species tested of which all the surviving animals circulated virus and developed neutralizing antibodies.
8.Of eight species tested against the French neurotropic strain only one, Nectomys squamipes, was found to be susceptible.
From the Laboratory of the Yellow Fever Research Service, Rio de Janeiro, Brazil.