The helix-coil transition kinetics of two 14-residue helical peptides of different stability were studied by time-resolved infrared (IR) spectroscopy coupled with laser-induced temperature-jump (T-jump) technique. The T-jump induced relaxation kinetics of both peptides show strong dependence on the final temperature, implying the existence of an enthalpic barrier for the nucleation process. In addition, the peptide with end-capping groups, which is more stable, folds faster. Together, these results suggest that the overall helical stability plays an important role in controlling the kinetics of the helix-coil transition, in agreement with results of early theoretical studies. (C) 2003 Elsevier Science B.V. All rights reserved.