The effect of monohydric alcohols on the micellization of several surfactants and on the thermal denaturation of lysozyme and of E-coli unfractioned t-RNA molecules, has been studied as a function of alcohol concentration in the water-rich region of composition. The results show that the effects due to alcohols on these very different systems and processes are strikingly similar and are closely linked with structural and dynamical properties of water-alcohol mixtures themselves. Accordingly, these results support the assumption that the dominant mechanism by which alcohols affect both the micellization process as the unfolding of proteins and nucleic acids molecules is through their effect on the properties of the solvent system. Available literature data suggest that the same conclusions could be valid for a number of other systems of biological and chemical interest.