Previously, we have described a serum-free insect cell culture medium, referred to as Efficient Medium for Insect Cell Growth (EMICG) (Ferrance et al., 1993). The medium supports cell growth to a high density and minimizes the formation of metabolic byproducts (e.g., ammonia and alanine) due to a tight coupling of energetic and biosynthetic demands. In this paper, we examine the ability of EMICG to support infection and recombinant protein production. Cells were infected with and without medium replacement at various densities with MOI values in the range 0.008-8. The experimental results revealed that the production of beta-galactosidase (model recombinant protein) was substantially higher (1.5-2.6-fold) in the EMICG cultures than the commercial SF-900 II medium. Moreover, beta-galactosidase levels achieved in EMICG are higher than those reported in the literature using other commercial media. Results of experiments in which medium was replaced at the time of infection indicate that the enhanced productivity may be due to lower production of toxic by-products in EMICG.