The equilibrium and nonequilibrium properties of an assembly of interacting spins are analyzed in the case of paramagnetism (nuclear). The evolution towards equilibrium is described by a generalized Pauli equation. This equation contains two relaxation times: a first one characterizing the evolution of the dipole-dipole system to equilibrium and a second one describing the energy exchange between the dipole-dipole and the Zeeman system. The real temperature of the system is the dipole-dipole one whereas the state of the Zeeman system is given by a "chemical potential" fixing the mean magnetic moment. It is shown that the Zeeman dipole-dipole relaxatin may also be considered as a kind of Brownian motion problem of a collective Zeeman coordinate in the "dipole-dipole heat bath."