The thermal stability of DNA and of ribonuclease and the pH stability of ordered poly‐L‐lysine conformation in salt (or buffer) aqueous solutions and in 2‐3 M hexa‐methylene tetramine (HMT) aqueous solutions have been found to be nearly identical, respectively. We have also found that HMT induces salting‐out of acetyltetraglycine ethyl ester in water and rises the melting point of aqueous gelatin gels.It is assumed that, despite its pronounced ability in inducing salting‐in in water of apolar molecule (1, 2) (a property shared by all common “denaturants”), HMT leaves the thermal stability of DNA and polypeptides essentially unaltered either because of a lack of direct interactions with the polyelectrolytes considered or because of unfavourable interactions with solvated peptide groups of the denaturat