At distinct potentials conformational transitions of adsorbed polynucleotides, especially double- and single-stranded DNA on the h.m.d.e. occur, recorded by a.c. polarographic current-time curves at the potential of peak 2. From the dependences of such fading reactions on potential, temperature, a.c. frequency, a.c. amplitude, ionic strength, pH value, complex formation and other effects, a coulombic model for DNA adsorption and compaction is established on the basis of current polyelectrolyte theory. The following steps are essential: 1. partial dehydration of adsorbed segments; 2. partial transition B → A form; 3. enhancement of fluctuation in base pairing; 4. compaction of neutralized DNA (π-state) by enhancement of cations in the vicinity of the electrode; 5. dissociation field effect on condensed counter ions in the attached parts of DNA; 6. direct and indirect (hopping mechanism) electron uptake, especially at lower pH values A.c-polarography (after Breyer) indicates certain transitions of tertiary structures, not only of adsorbed polynucleotides but also polyamino acids.