A series of 39 human brain tumors has been screened for the presence or absence of SV40-related T antigen by the direct and indirect immunoperoxidase methods. Two tumors of ependymal origin (malignant ependymoma, choroid plexus papilloma) revealed markedly positive nuclear staining for T antigen both in vivo and in vitro. The relationship of these tumors to their experimental counterparts inducible by recent human papovavirus isolates is discussed.