Several acute transforming retroviruses encode tyrosine-specific protein kinases which possess structural and functional relationships to cell-surface receptors for certain growth factors. One such tyrosine kinase is encoded by the onc gene, v-fgr, of Gardner-Rasheed feline sarcoma virus (GR-FeSV). Recently, we have isolated and characterized the human gene, c-fgr, corresponding to the viral onc sequence and have shown that c-fgr is a unique gene located on the short arm of chromosome 1 (ref. 7). Here we report that certain lymphomas (but not sarcomas or carcinomas) express fgr-related messenger RNA. This transcript is detected in Burkitt's lymphoma cell lines naturally infected with Epstein-Barr virus (EBV), but not in EBV-negative Burkitt's lymphoma cells. Normal umbilical cord or peripheral blood lymphocyte lines established in vitro by EBV infection also contain detectable c-fgr mRNA. Moreover, a 50-fold increase of the steady-state c-fgr mRNA concentration is observed when uninfected Burkitt's lymphoma cell lines are deliberately infected with EBV. These findings demonstrate for the first time the induction of a proto-oncogene in response to infection by a DNA tumour virus.