The baculovirus system has the potential for the large-scale production of protein products by two methods. First, as a result of recent advances (1,5), large-scale cell culture is now possible and, second, the recombinant baculovirus can be used to infect susceptible insect larvae (3). Whether using small-scale cell culture or the aforementioned methods for scale-up, the requirement for downstream processing of the protein product is manifest. Purification of the product is greatly facilitated when expression is high (ca. 30% of total cell protein); however, when expression is relatively low or membrane proteins are required, the researcher faces the same problems encountered in ascertaining the optimum conditions for any de novo protein purification. Obviously, the degree of purity required for a given product is indicative of its final use; consequently, a number of antigens for use in diagnostic procedures have been relatively crude preparations (4,5). This chapter highlights the methods that have been used to purify baculovirusexpressed protein products, and is aimed at providing general guidelines to the purification of certain types of protein product rather than a definitive guide to protein purification.