We have attempted to find out any relationships between circulating tumor necrosis factor (TNF)-alpha levels and Epstein-Barr virus (EBV) associated peripheral T-cell and NK-cell proliferative disease/lymphoma (PTPD/L) status. The distribution of TNF-alpha level was significantly higher (P<0.05) in patients than in controls. Patients carrying EBV genome in their peripheral T-cells showed higher TNF-alpha levels than the patients with EBV negative peripheral T-cells (P<0.001). Among patients whose peripheral T-cells were positive for EBV genome, TNF-alpha levels between the wild type LMP-1 gene carriers and the 30-bp deletion type LMP-1 gene carriers were compared and the wild type LMP-1 gene carrier group showed significantly higher TNF-alpha levels (P<0.01). As for the outcome of the patients and TNF-alpha levels, significant differences were observed between dead and alive with disease group (P<0.001), and dead and alive with complete remission group (P<0.01). Since circulating TNF-alpha levels in PTPD/L patients correlate with the disease and EBV infection status, it may be possible that monitoring of the TNF-alpha levels will be a useful prognostic marker.