When BmN-4 and M-BmN cells were grown in shake flasks, the pH initially dropped and later increased. The increase in pH signaled a ＇metabolic switch＇ that was used here as an indicator for initiating a supplemental glucose and glutamine feed. Using the pH-based fed-batch culture method described, the maximum cell densities of BmN-4 cells and M-BmN cells were increased from 30 x 10(5) cells ml(-1) to 43 x 10(5) and 52 x 10(5) cells ml(-1), respectively. Correspondingly, the production of polyhedra (45 x 10(5) OBs ml(-1)) and HBsAg (574 ng ml(-1)), from the infection of BmN-4 and M-BmN by wild-type and recombinant BmNPV viruses, respectively, were both significantly enhanced 50% and 100%, respectively. This feeding strategy was implemented with no advanced instrumentation yet facilitated significantly increased yield in shake flasks. The technique should benefit those in research laboratories employing the baculovirus expression system as a rapid and efficient production system.