Hodgkin's disease is commonly associated with EBV latent infection. The incidence of EBV reactivation (active infection or EBV infection with replicative cycle) was evaluated in a series of 30 patients with untreated Hodgkin's disease (except for one case with chronic lymphocytic leukemia) by quantitation of EBV DNA and titration of anti-ZEBRA antibodies in serum samples. DNA was detected in serum (>2.5 x 10(2) genomes/ml) in 15 of 30 patients and was more frequent in Hodgkin's disease with EBV-positive Reed-Sternberg cells (10/12) than in EBV-negative cases (5/18), (P< 0.01). Of interest was the demonstration that viremia correlated well with increased titers of anti-ZEBRA IgG and/or standard serological profiles of EBV reactivation (12/15), (P < 0.05). However the lack of EBV replicative cycle in Reed-Sternberg cells (negative for ZEBRA antigen and early antigen BHLF1) suggests that the viral replication occurs in a nonneoplastic cell compartment rather than in tumor cells. The measurement of EBV DNA loads and the titration of anti-ZEBRA antibodies shed new lights on the link between activation of EBV replication and Hodgkin's disease: these serological markers together with the determination of the EBV status of the tumor suggest that replication of the viral genome occurs with a decreased efficiency of the immune system, thus allowing progression of the tumor.