The capabilities of intra-cavity laser absorption spectroscopy associated with a high-resolution Fourier-transform spectrometer (FT-ICLAS) are investigated with a Ti:Sapphire laser. Weak absorption lines of atmospheric water were used to test the accuracy of absolute intensity measurements by FT-ICLAS leading to an excellent agreement (a few %) with the HITRAN data. The performances in terms of spectral resolution (0.028 cm(-1)) and sensitivity (2 x 10(-9) cm(-1)) are illustrated by the spectroscopic study of the overtone spectrum of (C2H2)-C-12 between 12250 and 12400 cm(-1) which allowed for a significant improvement of recent cavity ring-down measurements. Among the three Pi-Sigma bands rotationally analyzed, one is newly observed. The absolute intensity values of the bands are given. (C) 2003 Elsevier Science B.V. All rights reserved.