The usefulness of a method for detection of antibodies against Junin virus in whole blood was tested. N: NIH adult mice were inoculated with 10(3) PFU of attenuated XJ-Clon 3 Junin virus strain by intraperitoneal route and blood was obtained by retro-orbital puncture at 21 days post-infection. One blood aliquot (50 microliters) was collected in tubes containing a stabilizer solution for whole blood and another was processed for serum obtention. Immunofluorescent antibodies were tested on spot slides of a BHK/21 cell line persistently infected with Junin virus. High antibody titers (1/64 to 1/256) were detected in both whole blood and serum, with 66% coincidence between both procedures. These results show that the method of detection of antibodies in whole blood would be useful to test quickly for anti-Junin virus antibodies in seroepidemiologic studies, in endemic areas.