  The lifetime of the metastable 5d$^2$D$_{5/2}$ state has been measured for a
single trapped Ba$^+$ ion in a Paul trap in Ultra High Vacuum (UHV) in the
10$^{-10}$ mbar pressure range. A total of 5046 individual periods when the ion
was shelved in this state have been recorded. A preliminary value
$\tau_{D_{5/2}} = 26.4(1.7)$~s is obtained through extrapolation to zero
residual gas pressure.
