Abstract A full topological description of gelatin gels requires knowledge of the number, size and functionality of the helical segments, which act as effective junction zones. Selective enzymatic attack on renatured gelatin has allowed us to isolate the helical segments by size exclusion chromatography. For sharp fractions, the size of the helical segments is almost independent of initial molecular weight and is about 100–200 amino acid residues for each strand. This size does not depend very much on concentration, but increases slowly with renaturation time and with temperature. We believe that helical segments are always formed by the same process: in accordance with previous kinetic studies, the starting point would be a bimolecular nucleation. For such nucleation, two strands are necessarily antiparallel, and this can explain the limited length of the helices.