Examination of the primary tumor of glioblastoma multiforme and its recurrence for their association with JC virus revealed that, while the viral genome is present in both initial and recurrent tumors, expression of the viral oncoprotein T-antigen occurs only in the recurrent tumor cells. Accordingly, the level of inducible cellular transcription factors, including the p65 subunit of NF-kappaB and YB-1, which have the ability to stimulate JCV gene expression, was found to be higher in the recurrent tumor cells. These observations suggest that induction of the regulatory factors after resection of the primary tumor may have reactivated JC virus gene expression and led to redevelopment of the tumor in brain.