3 mM n-butyrate, which effectively induces synthesis of Epstein-Barr virus (EBV) antigens in the producer P3HR-1 cell line, inhibited the transformation of umbilical cord blood lymphocytes by EBV. The drug inhibited both EBNA synthesis and stimulation of host cell DNA synthesis by strain B95–8. This effect was less pronounced at lower concentrations, but even at 0.1 mM (which did not affect DNA synthesis in mitogen-stimulated lymphocytes or established lymphoblastoid cell lines) the synthesis of EBNA and stimulation of host cell DNA synthesis in EBV-infected lymphocytes were delaye