  By means of general kinematical arguments, the lifetime $\tau$ of a graviton
of energy $E$ for decay into gravitons is found to have the form $\tau^{-1} =
\frac{1}{EG} \sum_{j=1,2,...} c_j (\Lambda G)^j$. Some recent, preliminary
results of non perturbative simplicial quantum gravity are then employed to
estimate the effective values of $G$ and $\Lambda G$. It turns out that a short
lifetime of the graviton cannot be excluded.
