The development of cell-based assays for cellular receptors, ion channels, and transporters requires the delivery and expression of transgenes. Viral-mediated gene delivery is a particularly attractive approach for this purpose because of its efficiency and potential to deliver genes to a wide variety of cell types. Recombinant baculoviruses, long used to deliver genes to insect cells for overexpression, also effectively transfer genes to mammalian cells. The only required modification to the virus for this purpose is the addition of transgene expression cassettes controlled by mammalian cell-active promoters. These so-called BacMam viruses are useful for developing mammalian cell-based assays for investigating the function of recombinant proteins and for assessing the action of pharmacological modulators of their function. The use of such viruses is gaining popularity because of the ease of optimizing assay conditions, the ability to deliver multiple gene products, and of their flexibility in terms of host cells and levels of transgene expression. BacMam-mediated assays may be used for studying a wide variety of target proteins and assay technologies. Described in this unit is an example of BacMam-mediated gene delivery to configure a cell-based assay for pharmacological assessment of a G protein-coupled receptor. A protocol is also provided describing the use of a GFP-expressing BacMam to assess the susceptibility of new cell lines to transduction by the virus.