Immunopathological studies of the kidney, determination of circulating immune complexes and interferon blood levels were obtained in adult congenitally-athymic nude mice ((nu/nu) infected with lymphocyte choriomeningitis (LCM) virus as well as in their phenotypically-normal litter mates (nu/+). As previously reported, intracerebral or intraperitoneal infection in nu/nu mice did not induce any mortality and resulted in a carrier state characterized by persistently high levels of virus in the circulation. Interferon was present in the circulation for approximately 6 days. Circulating immune complexes were not detectable and glomerulonephritis assessed by light microscopy, electron microscopy and immunofluorescence, was either absent or very mild. These observations show that although a carrier state can be induced in adult nude mice, circulating immune complexes and glomerulonephritis do not develop. This situation is markedly different from that induced in normal Swiss mice infected at birth, which is characterized by raised levels of circulating immune complexes and development of glomerulonephritis in all infected mice.