  We study the contribution of the kinematic Sunyaev-Zel'dovich (kSZ) effect,
generated by the warm-hot intergalactic medium (WHIM), to the cosmic microwave
background (CMB) temperature anisotropies in the Five-Year Wilkinson Microwave
Anisotropy Probe (WMAP) data. We explore the concordance LambdaCDM cosmological
model, with and without this kSZ contribution, using a Markov chain Monte Carlo
algorithm. Our model requires a single extra parameter to describe this new
component. Our results show that the inclusion of the kSZ signal improves the
fit to the data without significantly altering the best-fit cosmological
parameters except Obh^2. The improvement is localized at the l>500 multipoles.
For the best-fit model, this extra component peaks at l~450 with an amplitude
of 129 muK^2, and represents 3.1% of the total power measured by the Wilkinson
Microwave Anisotropy Probe. Nevertheless, at the 2-sigma level a null kSZ
contribution is still compatible with the data. Part of the detected signal
could arise from unmasked point sources and/or Poissonianly distributed
foreground residuals. A statistically more significant detection requires the
wider frequency coverage and angular resolution of the forthcoming Planck
mission.
