The wide spectral coverage and high sensitivity of mode-locked cavity enhanced absorption spectroscopy (ML-CEAS) are illustrated by the observation of a very high overtone transition of C2H2 in the blue spectral region (420 nm, 8 quanta of CH stretch excitation), which was easily accessed by frequency-doubling a mode-locked femaosecond Ti:Sa laser. The detection limit is about 10(-8)/cm. The rotational analysis of this Sigma(u)(+)-Sigma(g+) parallel band, centred at 23 813.244 cm(-1), is presented and the vibrational assignment is discussed. (C) 2003 Elsevier B.V. All rights reserved.