The high resolution absorption spectrum of monodeuterated water, HDO, has been recorded by Intracavity Laser Absorption Spectroscopy (ICLAS) in the 12145–13160 cm 1 region. The achieved sensitivity (noise equivalent absorption on the order of amin 10 9 cm ) allowed detecting transitions with line strengths as weak as 10 27 cm/molecule which is about 50 times lower than the weakest line intensit...