For the production of a rVP2H vaccine, to protect young chickens from infection by an infectious bursal disease virus (IBDV), Trichoplusia ni (Hi-5) cells were cultured in a 500-ml spinner flask to evaluate the productivity of the rVP2H protein. The spinner flask, with a working volume of 500 mi, was equipped with a sparger to bubble the air at a flow rate of 0.134 vvm to provide adequate oxygen transfer. The oxygen transfer rate coefficient, k(L)a, was 24/h under these conditions. Hi-5 cells were grown and then infected with a recombinant rVP2H expressing baculovirus in spinner flasks. The Hi-5 cells generated a higher rVP2H yield at a low cell density (1 x 10(6) cells/ml) than at higher cell density (2-3 x 10(6) cells/ml). Nutrient depletion, especially glucose and glutamine, caused a decrease in specific productivity (i.e. production per cell) with increase in cell density at infection. A pH-based fed-batch culture method, in which the increase in pH, signalled by a ＇metabolic switch＇, was used as an indicator for initiating supplemental glucose and glutamine application. By applying this method, the production of rVP2H was increased from 25 to 54 mg/l when the Hi-5 cells were infected at a cell density of 2 x 10(6) cells/ml. This feeding strategy was carried out with simple instruments and could facilitate a significant increased-yield of rVP2H protein in spinner flasks. This technique should be beneficial in research laboratories employing the Hi-5 cells/baculovirus expression system as a rapid and efficient system for the production of foreign proteins. (C) 2000 Elsevier Science Ltd. All rights reserved.