Later in his career, Lifson was the principal collaborator in formulating the theory of the helix-coil transition in biological macromolecules, a process whose clarification is essential for understanding structural changes related to protein folding. Lifson then developed a method for calculating the interactions among the forces that various molecular components exert upon one another. Known as the consistent force field method, it makes it possible to characterize molecules in mathematical and physical terms, as well as to predict and calculate the energy of interaction among their components.