Starting from the Hubbard model with the repulsive Coulomb interaction and imperfectly nested Fermi surfaces we calculate the total, i.e. spin and charge density wave, 2kF-susceptibility above the critical temperature, taking into account both, orbital and spin coupling of electrons to the external magnetic field H. The influence of the magnetic field on the collective modes, and in particular the emerging splitting of degeneracies present in the isotropic case (H = 0), are also discussed