The following is a preliminary report of studies on yellow fever carried out by the West African Yellow Fever Commission of the Rockefeller Foundation. A detailed report, covering the work presented here as well as other studies on this subject, will be published shortly. During an epidemic of yellow fever at Larteh, Gold Coast, West Africa, in May, 1927, six Indian crown monkeys (Macacus sinicus) were inoculated with blood from patients with yellow fever. Five of these developed fever and died, while one did not show any reaction. From these five animals which died as a result of inoculation, three subinoculations were made into monkeys of the same species, two of which developed fever and recovered while one proved refractory. The gross and microscopic pathology in the five animals which died was somewhat suggestive of yellow fever, but in view of the fact that one monkey failed to succumb to