  Gravitational lensing by large scale structure introduces non-Gaussianity
into the Cosmic Microwave Background and imprints a new observable, which can
be used as a cosmological probe. We apply a four-point estimator to the
Wilkinson Microwave Anisotropy Probe (WMAP) 7-year coadded temperature maps
alone to reconstruct the gravitational lensing signal. The Gaussian bias is
simulated and subtracted, and the higher order bias is investigated. We measure
a gravitational lensing signal with a statistical amplitude of $\mathcal {C}$ =
$1.27\pm 0.98$ using all the correlations of the W- and V-band Differencing
Assemblies (DAs). We therefore conclude that WMAP 7-year data alone, can not
detect lensing.
