Selected human sera from 59 different !ocalities in Africa, the Mediterranean littoral, eastern Europe and Asia were examined by plaque reduction neutralization test against eight sandfly (Phlebotomus) fever virus serotypes (Sicilian, Naples, Arumowot, SudAn 754-61, Karimabad, Salehabad, Gordil and Saint Floris) known to occur in the Old World. Resulfs of these studies provide new information on the geographic distribution and prevalence of human infection with each of the viruses. Specific neutralizing antibodies were detected against a!! of the agents except Salehabad. Naples and Sicilian antibodies were encountered most frequently and had the widest geographic range ; moreover they were encountered most frequently and had the widest geographic range ; moreover they were found only in areas where Phlebotomus papatasi occurs. Age-specific antibody rates for several of the viruses are presented. These data and the epidemioiogy of sandfy fever are discussed.