IgG production kinetics of mouse myeloma MPC-11 cells immobilized within porous polyvinyl formal resin biomass support particles (BSPs) was evaluated by monitoring of lactate dehydrogenase activities and IgG concentration in a perfusion culture of the cells. Cells immobilized within the BSPs could stably maintain a high specific IgG production rate, comparable to the maximum production rate in a static culture of non-immobilized MPC-11 cells, over a long period.