Starburst polyamidoamine (PAMAM) dendrimers are a new class of synthetic polymers with unique structural and physical characteristics. These polymers were investigated for their ability to bind DNA and enhance DNA transfer and expression in various mammalian cell lines. Twenty different types of PAMAM dendrimers were synthesized, and their structures were confirmed using analytical techniques. The efficiency of plasmid DNA transfection using dendrimers was examined using two reporter gene systems: firefly luciferase and bacterial β-galactosidase. Transfections were performed using various dendrimers, and the levels of expression of the reporter protein were determined. Highly efficient transfection of a broad range of eukaryotic cells and cell lines was achieved with minimal cytotoxicity using DNA/dendrimer complexes. However, the ability to transfect cells was restricted to certain types of dendrimers and in some situations required the presence of additional compounds, such as DEAE-dextran, that appeared to alter the nature of the complex. A few cell lines demonstrated enhanced transfection with the addition of chloroquine, indicating endosomal localization of the complexes. The capability of a dendrimer to transfect cells appeared to depend on the size, shape, and number of primary amino groups on the surface of the polymer. However, the specific dendrimer most efficient in achieving transfection varied between different types of cells. These studies demonstrate that Starburst dendrimers can transfect a wide variety of cell types in vitro and offer an efficient method for producing permanently transfected cell lines. The introduction of genetic material into eukaryotic cells has been a major technique to investigate gene function and the regulation of gene expression. Recent advances in detecting inherited or acquired genetic disorders have provided the possibility of transferring recombinant genes into somatic cells to correct missing or defective gene products. A variety of methods have been developed to accomplish gene transfer into eukaryotic cells. These techniques involve the direct physical introduction of genetic material into cells, the disruption of cell membranes to allow the transfer of DNA, the use of genetically modified viruses to deliver genetic material, and the formation of DNA complexes with inorganic salts, polycations, or lipids to transfer the DNA across cell membranes. These techniques have great utility, but there are limitations in target cell type and in the ability to transfer different types of genetic material. Starburst PAMAM dendrimers are a new class of highly branched spherical polymers that are highly soluble in aqueous solution and have a unique surface of primary amino groups. Compared with many other types of dendritic macromolecules, PAMAM dendrimers are the only class of macromolecules that are unidispersed and show high charge densities restricted to the surface of the molecule. Dendrimers have been reliably produced in large quantities and can be precisely synthesized over a range of molecular weights similar to that of proteins. TheStarburst polyamidoamine (PAMAM) dendrimers are a new class of synthetic polymers with unique structural and physical characteristics. These polymers were investigated for their ability to bind DNA and enhance DNA transfer and expression in various mammalian cell lines. Twenty different types of PAMAM dendrimers were synthesized, and their structures were confirmed using analytical techniques. The efficiency of plasmid DNA transfection using dendrimers was examined using two reporter gene systems: firefly luciferase and bacterial β-galactosidase. Transfections were performed using various dendrimers, and the levels of expression of the reporter protein were determined. Highly efficient transfection of a broad range of eukaryotic cells and cell lines was achieved with minimal cytotoxicity using DNA/dendrimer complexes. However, the ability to transfect cells was restricted to certain types of dendrimers and in some situations required the presence of additional compounds, such as DEAE-dextran, that appeared to alter the nature of the complex. A few cell lines demonstrated enhanced transfection with the addition of chloroquine, indicating endosomal localization of the complexes. The capability of a dendrimer to transfect cells appeared to depend on the size, shape, and number of primary amino groups on the surface of the polymer. However, the specific dendrimer most efficient in achieving transfection varied between different types of cells. These studies demonstrate that Starburst dendrimers can transfect a wide variety of cell types in vitro and offer an efficient method for producing permanently transfected cell lines. The introduction of genetic material into eukaryotic cells has been a major technique to investigate gene function and the regulation of gene expression. Recent advances in detecting inherited or acquired genetic disorders have provided the possibility of transferring recombinant genes into somatic cells to correct missing or defective gene products. A variety of methods have been developed to accomplish gene transfer into eukaryotic cells. These techniques involve the direct physical introduction of genetic material into cells, the disruption of cell membranes to allow the transfer of DNA, the use of genetically modified viruses to deliver genetic material, and the formation of DNA complexes with inorganic salts, polycations, or lipids to transfer the DNA across cell membranes. These techniques have great utility, but there are limitations in target cell type and in the ability to transfer different types of genetic material. Starburst PAMAM dendrimers are a new class of highly branched spherical polymers that are highly soluble in aqueous solution and have a unique surface of primary amino groups. Compared with many other types of dendritic macromolecules, PAMAM dendrimers are the only class of macromolecules that are unidispersed and show high charge densities restricted to the surface of the molecule. Dendrimers have been reliably produced in large quantities and can be precisely synthesized over a range of molecular weights similar to that of proteins. The