Human sera samples from Córdoba Province, Argentina were analyzed by reduction neutralization test for Cache Valley (CVV) and Kairi (KRIV) viruses. A 5.72% (27/472) prevalence of neutralizing antibodies for CVV and 5.92% (31/524) for KRIV was detected in Córdoba City, whereas the prevalences in Jesús María and Colonia Caroya suburban cities was 7.83% (13/166) and 5.42% (9/166) for CVV and KRIV, respectively. The neutralizing antibody titers ranged between 1/20 and >or=1/160. Our results report the first known infection by CVV and KRIV in human inhabitants from temperate areas of Argentina.