French viscerotropic yellow fever virus will be transmitted by Caribbean Aedes aegypti to assess vector competence. Thai and Caribbean A. aegypti will be compared for competence to transmit Colombian dengue 2 virus. Cross neutralization tests with cloned rabies serogroup viruses will be done. The variables which affect VSV antigen sensitivity will be determined. Attempts will be made to produce improved hemagglutinating antigens for Crimean hemorrhagic fever-Congo (CHF-C) virus strains other than C 3010 and IbAr 10200. If successful, strains will be compared by kinetic HI tests. Cross neutralization tests will be done with CHF-C viruses using acetone-ether extraction of sera. Anti serum-inhibitory-substance (SIS) will be used experimentally to remove SIS from sera. The techniques developed for removal of CHF-C inhibitory substance will be applied to other tick-borne viruses.