  We consider the change of entanglement of formation $\Delta E$ produced by
the Hadamard-CNOT circuit on a general (pure or mixed) state $\rho$ describing
a system of two qubits. We study numerically the probabilities of obtaining
different values of $\Delta E$, assuming that the initial state is randomly
distributed in the space of all states according to the product measure
recently introduced by Zyczkowski {\it et al.} [Phys. Rev. A {\bf 58} (1998)
883].
