Human immunodeficiency virus type 1-based defective lentiviral vectors (HIV-based vector) efficiently transduce a wide range of mammalian cell types, but little is known with respect to their utility for gene transfer applications involving primary mouse monocytes/macrophages. This may be important for preclinical development of a range of potential gene therapeutic modalities. Present study described the development of an optimized method for viral vector-mediated gene transfer into primary mouse monocytes/macrophages and the establishment of reproducible protocols for cell isolation/cultivation. It has been determined that bone marrow-derived monocytes/macrophages were consistently more susceptible to viral vector-mediated gene transduction, as compared to blood-derived cells. It has also been documented that the efficiency of transduction increased when cells were maintained in vitro, prior to exposure to vector virus. Finally, experiments were conducted to compare the efficiency of gene transfer mediated by HIV-based vectors to that achieved by other lentivirus or retrovirus vector systems. These studies showed that HIV-based vector system was consistently superior. Overall, these results establish a new and efficient method for gene transfer into primary mouse monocytes/macrophages. This may be of utility in the preclinical development of gene therapies that target this important cell type.