Studies of the gene expression, metabolism and intracellular signaling of adipocytes have been hindered by the difficulty of transfecting cultured adipocytes using standard methods. Here, we demonstrate the utility of gene gun-mediated genetic transfer for transfection of differentiated 3T3-L1 adipocytes. Transfection of adipocytes with the Helios Gene Gun yielded a transfection efficiency that was consistently 5%-10% of total cells. We have used this technique to overexpress the transcription factor CCAAT/Enhancer Binding Protein alpha (C/EBP alpha) and transactivate an obese gene promoter-luciferase construct. This method has broad utility for transfection of other cell types that are resistant to transfection.