Abstract: A composition for delivering a biologically active polyanionic molecule comprising a linear polymer with a backbone comprising amido and tertiary amino groups arranged regularly on the backbone and biologically active polyanionic molecule bound to the polymer. Preferably, the linear polymer comprises a poly(amidoamine). Preferably, the biologically active polyanionic molecule is a nucleic acid, more preferably a DNA. The compositions are useful for delivering nucleic acids to a cell in a cell transformation, transfection or gene therapy method.