Yields of cell and baculovirus-expressed recombinant protein in Sf-9 cultures were improved using fed-batch addition of glucose, amino acids, lipids, yeastolate ultrafiltrate, vitamins, iron and trace metals. Using this approach, the highest maximum cell and recombinant p-galactosidase volumetric yields obtained, 3 x 10(7).ml(-1) and 900 units.ml(-1), respectively, were both approximately triple their respective values in unamended cultures.