So-called fowl glioma is characterized by multiple nodular gliomatous growths associated with disseminated non-suppurative encephalitis. To investigate the possibility of the induction of the gliomatous lesions, chicks of Japanese bantams (Gallus gallus domesticus) and specific pathogen free chickens (C/O strain White Leghorn) were intracerebrally inoculated with a brain homogenate or culture supernatant from a bantam affected with fowl glioma. All bantams and 16 chickens (89%) in the inoculated groups showed non-suppurative encephalitis, and the 18 bantams (82%) and five chickens (28%) developed multiple nodules consisting of aggregations of astrocytes in the cerebrum. These astrocytes had avian leukosis virus (ALV) antigen. By Southern blot analysis, the ALV sequence was detected both in DNA prepared from the brains of the inoculated birds and in DNA from the inoculum. Ultrastructurally, tadpole-shaped particles, approximately 100 nm in diameter, were detected in the concentrated supernatant of the chicken embryo fibroblasts, and budding of the particles was noted. These results substantiated that fowl glioma of the bantams could be transmitted by intracerebral inoculation of the affected tissue and that the causal agent was an unidentified strain of ALV.