Levine, Gordon, and Jencks's 53 studied at constant temperature (73 • C) the effectiveness of a broad spectrum of chemicals as denaturing agents (See Table ). These authors show the dependence of the denaturation degree, K, for T 4 bacteriophage DNA from the concentration of denaturants M, expressed in M ol/l. They found the concentration for each additive M Tm corresponding to 50 percent DNA denaturation that equals K = 1. These data are also presented in Table .