Obesity is associated with many serious afflictions such as cardiovascular disease, cancer, and diabetes. One of the main cellular systems used to study the underlying physiological and biological processes is the 3T3-L1 preadipocyte differentiation model. However, studies on 3T3-L1 adipocytes are hampered by the fact that genetic modification of mature adipocytes is notoriously difficult. In this report, we evaluated the use of lentivirus-mediated gene transfer into 3T3-L1 mature adipocytes. We demonstrate that quiescent, fully differentiated 3T3-L1 adipocytes as well as 3T3-L1 preadipocytes can be efficiently transduced with HIV-1-derived lentiviral vectors. Upon transduction using LV-PGK-GFP lentiviral vector at 100 ng p24 per 10(5) cells, more than 95% of the 3T3-L1 adipocytes in the culture expressed the GFP reporter gene. There were no overt signs of toxicity or cytopathogenicity in the cultures. Furthermore, modification of undifferentiated preadipocytes did not affect their capacity to differentiate. In addition, insulin-induced glucose uptake was not affected by the procedure. In contrast, adenoviral-mediated gene transfer into 3T3-L1 adipocytes is associated with marked cytopathogenicity. From these data, we conclude that lentiviral vectors are the gene-transfer system of choice for genetic modification of mature adipocytes. The availability of an efficient vector system may stimulate the use of adipose tissue as a target for gene therapy in obesity and other disorders.