The aim of the present work is to assess whether reactivation of viral replication occurred in children affected by chronic hepatitis undergoing long term immunosuppressive therapy. 123 serum samples belonging to 25 children were retrospectively evaluated for HBV-DNA and HBeAg. Sera were collected prior to and during the protocol treatment (steroids alone or with azathioprine). Presence of HBV-DNA was evaluated by means of molecular hybridization technique, using a radiolabelled probe of cloned HBV-DNA. Sera (100 1) were denatured and transferred into nylon membrane (spot) then prehybridized and hybridized. After washing in stringent conditions, the filter was exposed in autoradiographic cassette with Kodak film XOmat5. Positivity was semiquantitatively evaluated by blackening of the spot. Increase or appearance of HBV-DNA was observed in the sera from 24/25 pts. HBeAg became positive in 4/5 pts previously negative. Obtained data shows reactivation of viral replication during immunosuppressive therapy. Data are especially significant in those cases in which such activity has apparently ceased or not been detected; HBV may be considered as a latent virus.