Summary Attempts were made to transmit yellow fever with seven different species of mosquitoes, viz., Aedes luteocephalus, Aedes apicoannulatus, Aedes apicoargenteus, Aedes longipalpis, Aedes welmani, Culex nebulosus and Eretmopodites chrysogaster with the following results: 1. A. luteocephalus and A. apicoannulatus transmitted this disease in all respects in the same manner as A. aegypti. 2. Two lots of E. chrysogaster were allowed to feed on infected monkeys. One of these lots produced typical infection when later fed on normal monkeys; the mosquitoes of the other lot failed to convey the virus through bite, but proved infective when macerated and injected into a normal monkey twenty-four days after their original infecting feed. 3. Attempts to transmit the disease with A. apicoargenteus gave entirely negative results, both by biting experiments as well as by the injection of the bodies of these mosquitoes into normal monkeys at various intervals after they were fed on infected animals. 4. A. longipalpis, A. welmani and Culex nebulosus failed to feed on infected monkeys, and the question as to whether these insects are capable of transmitting yellow fever could not be determined. 5. The pathological findings in the monkeys which died after being bitten by A. luteocephalus, A. apicoannulatus and E. chrysogaster were typical of yellow fever, and the virus was apparently not modified or its virulence attenuated by the passage through these mosquitoes.