Development and application of an in vitro model for screening anti-hepatitis B virus therapeutics. The development of effective anti-hepatitis B virus agents has been hampered by the lack of reliable in vitro systems for the screening of new therapeutics. In an effort to circumvent this problem, we have developed an in vitro system for screening anti-hepatitis B virus drugs using hepatitis B virus DNA-transfected Hep G2 cells. The cell line designated 2.2.15 produces replicative viral DNA intermediates, mature Dane particles and high levels of viral antigens. Subconfluent 2.2.15 cells were treated with a variety of commonly used anti-hepatitis B virus therapeutics, and their efficacy was determined by analyzing changes in the replicative cellular or extracellular hepatitis B virus DNA content by Southern blotting or slot-blot hybridization. The slot-blot method was sensitive, reproducible and rapid and correlated well with Southern blotting. Analysis of the media for hepatitis B virus DNA was indicative of changes in intracellular, replicative hepatitis B virus DNA, permitting sampling of the media. Therefore 2.2.15 cells may provide a valuable method for identifying and monitoring effective anti-hepatitis B virus therapeutics. Using this system to test various agents, we confirm that 2'-deoxyguanosine strongly inhibited viral replication, whereas others tested were less effective. Correlation with in vivo systems is now needed. 