Spodoptera frugiperda (Sf-9) insect cells were immobilized and cultured on a fibrous matrix. This technique has been already exploited for plant and mammalian cell culture. Its advantages lie in its ease and efficiency of cell attachment and its feature to segregate cell and medium components of the culture thus allowing for easy semi-continuous or continuous operation, as well as facilitating product recuperation from the medium without cell washout. Immobilization onto the matrix also permits physical stabilization of insect cells. Infected Sf-9 cells, by baculovirus (Autographa californica nuclear polyhedrosis virus), are known to be especially sensitive to the mechanical stresses of the culture environment. First work is presented showing nutrient consumption, metabolite production and respiration patterns of immobilized uninfected and infected insect cell cultures. Maximum immobilized cell densities reached 2.47 x lO 6 cells/ml or density of 2.47 x lO 6 cells/cm 2 of gross surface area of the immobilizing matrix. A recombinant baculovirus coding for secreted wildtype papain was used to infect a 21 immobilized insect cell bioreactor culture which produced active papain enzyme at about 75% of the yield typically found in equivalent suspension cultures.