In response to the criticism by A. Finkelstein (J. Biomol. Struct. Dyn. 20, 311-314, 2002) of our Communication (J. Biomol. Struct. Dyn. 20, 5-6, 2002) several issues are dealt with. Importance of the notion of elementary folding unit, its size and structure, and the necessity of further characterization of the units for the elucidation of the protein folding in vivo are discussed. The criticism (J. Biomol. Struct. Dyn. 20, 311-314, 2002) on the hierarchical protein folding is also briefly addressed.

Key words: Levinthal paradox; folding units; protein folding, biological relevance.