A proof of reciprocity relations for nonlinear systems ininhomogeneous variable electric and magnetic fields in the presence ofunsteady spin currents, thermodynamic flows and mechanical disturbances isobtained by the Kubo method in the approximation of Markov relaxation andlocally quasi-equilibrium distribution. Keywords: Nonlinear distributed systems, locally quasi-equilibrium distribution, Markov relaxation, spin current, reciprocity\