  We present studies of the collapse of neutron stars that undergo a
hadron-quark phase transition. A spherical Lagrangian hydrodynamic code has
been written. As initial condition we take different neutron star
configurations taking into account its density, energy density and pressure
distribution. The phase transition is imposed at different evolution times. We
have found that a significant amount of matter on the surface can be ejected
while the remaining star rings in the fundamental and first pressure modes.
