In this paper we consider the nonlinearly damped semilinear wave equation
u(tt) - Deltau + au(t)\u(t)\ (m-2) = bu \u \ (p-2)
associated with initial and Dirichlet boundary conditions. We prove that an
y strong solution, with negative initial energy, blows up in finite time if
p>m. This result improves an earlier one in [2].