AbstractBinding of the hydrophobia fluorescent probe, 1‐anilino‐naphthalene‐8‐sulfonate (ANS), to synthetic polypeptides and proteins with a different structural organization has been studied. It has been shown that ANS has a much stronger affinity to the protein “molten globule” state, with a pronounced secondary structure and compactness, but without a tightly packed tertiary structure as compared with its affinity to the native and coil‐like proteins, or to coil‐like, α‐helical, or β‐structural hydrophilic homopolypeptides.The possibility of using ANS for the study of equilibrium and kinetic molten globule intermediates is demonstrated, with carbonic anhydrase, β‐lactamase, and