Quantum and collisional effects on the unstable spectrum of a relativistic electron beam–plasma system are investigated through a two-fluids model. Application is made to the near target center interaction of the relativistic electron beam in the fast ignition scenario. Partial degeneracy effects are found to be negligible while the most influential factors are the beam temperature and the electron–ion collision frequency of the plasma. The introduction of the latter triggers some oblique unstable modes of much larger wavelength than the collisionless ones. Transition from the collisionless regime to the resistive one is thus documented and found discontinuous.