  We consider the inverse problem of determining a time-dependent potential
$q$, appearing in the wave equation $\partial_t^2u-\Delta u+q(t,x)u=0$ in
$Q=(0,T)\times\Omega$ with $\Omega$ a $C^2$ bounded domain of $\mathbb R^n$,
$n\geq2$, from partial observations of the solutions on $\partial Q$. We prove
global unique determination of a coefficient $q\in L^\infty(Q)$ from these
observations.
