  The search for events containing isolated leptons (electrons or muons) and
missing transverse momentum produced in $e^{\pm}p$ collisions is performed with
the H1 detector at HERA in the period 1994--2005. The analysed data sample
corresponds to an integrated luminosity of 279 pb$^{-1}$, which includes 53
pb$^{-1}$ of $e^{+}p$ data and 107 pb$^{-1}$ of $e^{-}p$ data from the new
HERA~II phase. A total of 40 events are observed in the data, compared to a
Standard Model (SM) prediction of 34.3 $\pm$ 4.8. At large hadronic transverse
momentum $P_{T}^{X} >$ 25 GeV, a total of 17 events are observed compared to
9.0 $\pm$ 1.5 predicted by the SM. In this region, 15 events are observed in
the $e^{+}p$ data compared to a SM prediction of 4.6 $\pm$ 0.8, whereas in the
$e^{-}p$ data 2 events are observed compared to a SM prediction of 4.4 $\pm$
0.7.
