2-day-old Wistar rats intracerebrally infected with the XJC13 strain of Junin virus exhibited a 5% survival rate which rose to 71 % after immune serum treatment. Brain viral titers were relatively unaffected by this treatment. Histologic studies showed necrosis in the cerebellum and brain cortex with mononuclear cell infiltration in both treated and nontreated groups. Beginning on day 16 postinfection, however, intracerebral perivascular gliosis foci and mild meningeal congestion were minimal in the treated animals. These findings imply that passively transferred humoral immunity leads to prompt recovery in this experimental model.