We show the presence of a strong negative feedback effect in the vibrational relaxation of the O-H stretch vibrations of liquid H2O. The vibrational relaxation of an O-H stretch vibration leads to the excitation of strongly coupled low-frequency modes, which induces a deceleration of the relaxation of other still excited vibrations. We present a model for this feedback effect, with which we obtain a consistent interpretation of the experimental results of recently reported femtosecond mid-infrared pump-probe experiments and mid-infrared pump anti-Stokes Raman probe experiments. (C) 2003 Elsevier B.V. All rights reserved.