Weanling Fischer rats inoculated intramuscularly with Hantaan virus (strain 76-118) developed subclinical infections characterized by transient viremia and shedding of virus in saliva, persistence of virus in lung, pancreas, spleen and liver, and development of fluorescent and neutralizing antibodies in serum with immune complex deposition in lung. Viremia and virus shedding in saliva occurred 10 to 13 days after inoculation. Horizontal intracage transmission of infection occurred between 35 and 63 days post-inoculation, long after disappearance of virus in oropharyngeal secretions and blood. Multiple attempts to demonstrate infectious virus in feces and urine during this period were unsuccessful. The inability to detect virus in urine samples of experimentally infected rats may have resulted from intermittent or low-titered viruria. This contrasts sharply with the prolonged high-titered viruria reported in striped field mice (Apodemus agrarius) infected with Hantaan virus, suggesting differences in the mode(s) of virus transmission in nature.