Akata and Mutu cell lines are derived from Burkitt's lymphoma (BL) and retain the in vivo phenotype of Epstein-Barr virus (EBV) expression that is characterized by expression of EBV-determined nuclear antigen 1 (EBNA1), EBV-encoded RNAs (EBERs) and transcripts from the BAM:HI A region (BARF0). We found that EBV-positive Akata and Mutu cell clones expressed higher levels of interleukin (IL)-10 than their EBV-negative subclones at the transcriptional level. Transfection of an individual EBV latent gene into EBV-negative Akata cells revealed that EBERs were responsible for IL-10 induction. Recombinant IL-10 enabled EBV-negative Akata cells to grow in low (0.1%) serum conditions. On the other hand, growth of EBV-positive Akata cells was blocked by treatment either with an anti-IL-10 antibody or antisense oligonucleotide against IL-10. EBV-positive BL biopsies consistently expressed IL-10, but EBV-negative BL biopsies did not. These results suggest that IL-10 induced by EBERs acts as an autocrine growth factor for BL. EBERs, EBER1 and EBER2, are non-polyadenylated RNAs and are 166 and 172 nucleotides long, respectively. The present findings indicate that RNA molecules could regulate cell growth.