This paper describes a preliminary evaluation of particle-mediated bombardment via the Helios gene gun for the delivery of therapeutic genes to synovial cells in culture. A reporter gene, enhanced green fluorescent protein, was delivered to rabbit synovial fibroblasts (hig-82) using gold particle (1·0 μm) bombardment to evaluate transfection efficiency at helium pressures of 100 and 150 psi. Transfection of cells occurred at these pressures despite some cell death. The in vitro delivery of gold particles to samples of synovial membrane and articular cartilage from a freshly euthanased dog was also studied to examine depth of penetration of gold particles (1·0 μm) at helium pressures of 250 and 500 psi. Light microscopical examination of histological sections of the synovial membrane showed that particles of gold had penetrated the lining cells of the synovium. However, no gold particles had penetrated the articular cartilage even at 500 psi.