Although gene therapy holds great promise for the treatment of both acquired and genetic diseases, its development has been limited by practical considerations. Non-viral efficacy of delivery remains quite poor. We are investigating the feasibility of a novel lipid-based delivery system, cochleates, to deliver transgenes to mammalian cells. Rhodamine-labelled empty cochleates were incubated with two cell-lines (4T1 adenocarcinoma and H36.12 macrophage hybridoma) and primary macrophages in vitro and in vivo. Cochleates containing green fluorescent protein (GFP) expression plasmid were incubated with 4T1 adenocarcinoma cells. Cellular uptake of labelled cochleates or transgene GFP expression were visualised with fluorescence microscopy. 4T1 and H36.12 lines showed 39% and 23.1% uptake of rhodamine-cochleates, respectively. Human monocyte-derived macrophages and mouse peritoneal macrophages had 48+/-5.38% and 51.46+/-15.6% uptake of rhodamine-cochleates in vitro. In vivo 25.69+/-0.127% of peritoneal macrophages were rhodamine-positive after intra-peritoneal injection of rhodamine-cochleates. 19.49+/-10.12% of 4T1 cells expressed GFP. Cochleates may therefore be an effective, non-toxic and non-immunogenic method to introduce transgenes in vitro and in vivo.