Lipid-based DNA transfer formulations are typically selected on the basis of in vitro transfection studies where the activity of specific formulations is defined by transgene expression. It is unclear, however, whether expression is directly related to the efficiency of DNA transfer. In an attempt to correlate DNA transfer with transgene expression, we used a simple assay consisting of measuring DNA (3H-plasmid encoding for beta-galactosidase) binding to murine (B16/BL6) and human (KZ) melanoma cells in vitro at 4 and 37 degrees C. The difference in cell association at these temperatures was assumed to be a consequence of DNA uptake, an assumption that was confirmed by protease removal of cell surface-associated DNA. DNA associated with B16/BL6 melanoma cells (up to 30 ng or 12% of the added DNA) following incubation with dioleoyldimethylammonium chloride/dioleoylphosphatidylethanolamine (DOPE) liposome-DNA aggregates was comparable to that achieved with 1,2-dioleoyloxypropyl-3-trimethylammonium bromide/DOPE or dimethyldioctadecylammonium bromide/DOPE liposomes; however, transgene expression was 2- and 5-fold less for the latter two formulations, respectively. Similarly, equivalent amounts of DNA delivery were achieved with B16/BL6 and KZ melanoma cells, yet the level of transgene expression in the KZ cells was undetectable. It was demonstrated that the lack of transgene expression was not a consequence of cell-specific differences in DNA degradation.