Cultured insect cells have many uses in agriculture and medicine. They can be used in the diagnosis and isolation of a number of viruses infecting both animals and plants and for the laboratory study of these viruses. Large-volume culture of insect cells has been envisioned as a way of producing viruses for use in controlling insect pests and for the production of viral antigens for vaccine preparations. Recently they have become a potentially valuable way of producing a variety of proteins for human and veterinary medicine using the genetically engineered baculovirus expression vectors. The development of satisfactory cell lines and culture methods has proceeded at a slow, irregular pace, inhibited by the lack of knowledge of the physiology of the insect, its small size, and often by the lack of consistent, adequate support for the necessary developmental research. However, now that the basic culture systems are available, cell lines have been developed or can easily be developed for most needs. Suitable media are available and recent developments in refining existing media formations have resulted in low-cost media containing little protein to interfere with down-stream processing of cellular metabolites. Future developments are likely to further improve the media formulations and lower the cost. Technical problems relating to oxygen demand and cell fragility that inhibited the continued development of large-volume culture systems beyond the laboratory a few years ago now appear to be solved or at least are solvable. The successful culture of the Spodoptera cells in bioreactors of 40-liter capacity indicates that means of producing insect cells or their metabolic products on a commercial scale can be made economically feasible.