The v-myc oncogene can induce tumours in haematopoietic, mesenchymal and epithelial tissues1. The corresponding c-myc proto-oncogene can contribute to the genesis and/or the progression of an equally wide variety of tumours when activated by retroviral insertions, chromosomal translocations or gene amplification2. The c-myc gene product is a DNA-binding, nuclear phosphoprotein that is involved in the control of cell proliferation and possibly in DNA synthesis2. The replication of Simian virus 40 (SV40) is a useful model system to study eukaryotic DNA replication as the virus relies almost entirely on cellular DNA replication apparatus. The SV40-based vector, pSVEpR4, replicates poorly in the human BJAB lymphoma line and in most human cells, but replicates well in Burkitt lymphoma lines, which have fused immunoglobulin and c-myc genes, resulting in high c-myc expression. Cotransfection of the BJAB cells with a c-myc-expressing construct (pI4-P6) increased the replication of pSVEpR4 tenfold. Our findings indicate that overexpression of the c-myc gene product allows the replication of SV40 in human lymphoma cells, suggesting that c-myc is involved in the control of replication.