Abstract : The objectives of the contract are to develop new diagnostic procedures and new vaccine strategies pertinent to selected Phlebotomus fever (PHL) group viruses, viruses that constitute the Phlebovirus genus of the negative sense RNA virus family Bunyaviridae. The development of new diagnostic tools for the specific identification of PHL group viruses is being investigated using eukaryotic expression vectors and cDNA clones of particular phlebovirus genes that are being prepared or that are available to us. Two expression systems are under study, vaccinia and the insect specific baculovirus expression vectors. So far, it has proven difficult to express the complete M RNA gene products of Punta Toro (PT) phlebovirus using either vector. Recombinant vaccinia viruses have, however, been made that express part of the PT M RNA, producing the PT glycoproteins G1 and G2. The expressed products have been characterized. The expression of PT S RNA gene products, using Autograph californica nuclear polyhedrosis virus (AcNPV) baculovirus vectors also been reported. The objective of developing new vaccine strategies for PHL group viruses is being realized through the characterization of an attenuated, candidate vaccine derivative of Rift valley fever (RVF) phlebovirus (the M12 mutant of RVFV isolate ZZ548). The complete sequence of the viral M RNA of the M12 RVFV derivative has been obtained. The M RNA of the RVFV M12 derivative has been expressed in baculovirus vectors and the products characterized.