A novel gene transfer system that complexes plasmid DNA (pDNA) through complementary hydrogen bonding of guests with base pairs is reported. Poly(vinyldiaminotriazine) (PVDT) homopolymer and its copolymers with poly(1-vinyl-2-pyrrolidone) are synthesized via conventional radical random polymerization, and water-soluble fractions are collected. These PVDT-based polymers efficiently complex pDNA and displace ethidium bromide (EB) in EB-intercalated pDNA solutions because of the hydrogen-bonding-induced constrained state of pDNA. It is also found that upon complexation, pDNA seems to undergo B-C conformation change and circular dichroism spectra assumed a polymer-and-salt-induced (psi)-type pattern that is rationally ascribed to a certain change in the high-order structure of DNA condensates. Transmission electron microscopy presented several morphologies of spheres and toroids within aggregates >= 100 run, resembling DNA condensation induced by cationics. In transfection studies using pDNA-encoding luciferase or enhanced green fluorescent protein, this system could efficiently transfect COS-1 cells. Compared to the commercial polycation system, ExGen 500, these H-bonding vectors display several merits such as higher transfection efficiency, lower cytotoxicity, better serum compatibility, and stability in the presence of bovine serum albumin (BSA). The results suggest that PVDT-based polymers are superior to polycation counterparts with regard to their potential in vivo applications.