Results show that for chemical denaturation of T4 bacteriophage DNA, the effect of hydrogen bonding is the dominant part of enthalpy (67%). Table also indicates that dispersion forces have the lowest influence on enthalpy (11%). This direct experimental data is opposite to the conclusions presented by A.Dragan, Crane-Robinson, and P.Privalov (see introduction, ) related to the thermostability of DNA in the absence of denaturants.