1. We have developed a theory describing the chemical denaturation of DNA for low and medium denaturation degrees, including but not limited to 50% denaturation, as a reversible first-order reaction. The theory had no adjustable parameters; all parameters were known from independent data, and the theory was supported experimentally. This theory, with experimental data, shows the degree of influence of hydrogen bonding, dispersion, polar forces, proton donor/acceptor ratio, dipole induction, orientation parameter, and electrostatic interaction during DNA denaturation. The theory links the degree of DNA denaturation with the concentration of denaturants, Hildebrand, Hansen, KSE cohesion parameters, and temperature.