Viruses in the Phlebovirus genus of the family Bunyaviridae cause clinical syndromes ranging from a short, self-limiting febrile illness to fatal haemorrhagic fever. The genus currently consists of 68 antigenically distinct virus serotypes, most of which have not been genetically characterized. RT-PCR with four 'cocktail' primers was performed to amplify a region of the M segment of the genome of 24 phleboviruses included in the sandfly fever Naples, sandfly fever Sicilian and Punta Toro serocomplexes. Partial M segment sequences were successfully obtained and phylogenetic analysis was performed. The three resultant genotypic lineages were consistent with serological data. The sequence divergences were 27?6 % (nucleotide) and 25?7 % (amino acid) within the Sicilian serocomplex, 33?7 % (nucleotide) and 34?4 % (amino acid) within the Naples serocomplex and 35?6 % (nucleotide) and 37?5 % (amino acid) within the Punta Toro serocomplex. Overall, the diversities among viruses of Sicilian, Naples and Punta Toro serocomplexes were 48?2 % and 57?6 % at the nucleotide and amino acid levels, respectively. This high genetic divergence may explain the difficulties in designing a consensus primer pair for the amplification of all the phleboviruses using RT-PCR. It also suggests that infection with one genotype may not completely immunize against infection with all other genotypes in a given serocomplex. These findings have implications for potential vaccine development and may help explain clinical reports of multiple episodes of sandfly fever in the same individual.