Spodoptera frugiperda (Sf-9) insect cells are fully capable of growth and proliferation in a glutamine, glutamate and aspartate-free medium, provided that ammonium ions are supplied. S. frugiperda (Sf-21) and Mamestra brassicae cells (IZD-MB-0503) also grow in glutamine-free media but not Trichoplusia ni cells (BTI-TN 5B 1-4). The yield of beta-galactosidase in Sf-9 cells infected with a recombinant baculovirus under glutamine-free conditions was even higher than the yield obtained in glutamine containing cultures.