Neonatal Calomys musculinus experimental infection with Junín virus (JV) XJCl3 strain causes either death or a persistent infection in the major part of surviving animals. JV can be isolated from peritoneal macrophages early during infection, and from brain and salivary glands during the chronic state of disease. It was of interest to investigate the appearance of virus in blood of infected animals. For this purpose, we decided to study the development of viremia in inoculated cricetids. A high frequency of viremia was registered during the acute state of disease (figure 1), which became sporadic approximately from 20 days post-infection onwards. Considering the results above mentioned, the characteristic lymphotropism of arenaviruses and the well-known JV replication in human mononuclear cells, cultures of lympho-monocytes obtained from blood of infected C. musculinus were done in order to investigate the eventual detection of infectious virus in the supernatants. JV was isolated, although in low titres, from cultures established with mononuclear cells belonging to animals in the acute state of disease (table 1); in the case of chronically infected cricetids, attempts to isolate JV were negative. These results show that viremia is currently detected in experimentally infected C. musculinus and that circulating mononuclear cells are permissive for JV multiplication, during the acute state of disease.