Thirty-four primary (untreated) patients with non-Hodgkin's lymphomas (NHL) infected with Epstein-Barr virus (EBV) were examined. Their HLA phenotype and the production of interleukin-1 beta and tumor necrosis factor alpha were assessed. Serological profiles characteristic of the late stages and reactivation of EBV infection were detected in 16(47.1%) patients. NHL of low malignancy predominated in EBV-infected patients. A greater number of blank HLA-A antigens and a higher incidence of HLA-DR7 antigen was observed in infected patients. Serum concentration of tumor necrosis factor a was reliably higher in them, whereas the production of this cytokine by the peripheral blood mononuclears decreased. Hence, serum tumor necrosis factor is a product of transformed B lymphocytes. Spontaneous and stimulated production of interleukin-1 beta by peripheral blood mononuclears was significantly decreased in EBV-infected patients, and the serum concentration of this cytokine similarly had a trend to decrease, which indicates an inhibition of Interleukin-1 beta production in EBV-infected patients with NHL.