The hepatitis B virus (HBV) S gene, PreS2 + S genes and the late phase expression cassette (MTI) + HBV S genes were separately cloned into Ad5 vector downstream of E3 promoter (pAd5 deltaE3 provided by Wyeth Co.). The above constructed plasmids and Ad5 DNA EcoR I A fragment were cotransfected into 293 cells. The progeny adenoviruses named rAd5S, rAd5MS, rAd5S2S were harvested for analysis. The recombinants were isolated and analyzed by PCR, using two primers specific to the HBV S genes. The expressed products were detected by ELISA and RIA. The recombinant containing MIT + HBV S genes (rAd5MS) was identified to be ELISA positive, whereas the other two recombinants (rAd5S, rAd5S2S) were negative to ELISA, but positive to RIA. The results indicated that adenovirus E3 early promoter could express the inserted foreign genes, and MIT worked well in the E3 region of Ad5 and could increase the expression capacity of the recombinants. The conditions for foreign gene expression and genetic stability of the recombinant viruses were studied in detail. There was no wild Ad5 discovered during the cotransfection experiments. The present study provides some experiences for studying adenovirus recombination.