The effects of silkworm hemolymph on the expression of foreign genes by recombinant baculoviruses in cell lines were studied. The expression efficiency of beta-galactosidase by recombinant virus containing the E. coli lacZ gene at various concentrations of hemolymph and FBS was determined in BmN and Sf cell lines. The addition of hemolymph to the medium containing FBS accelerated the expression of beta-galactosidase by recombinant viruses in both cells. It was more effective in BmN cells than in Sf cells. Hemolymph was most effective in enhancing virus multiplicity under conditions of 5% FBS.