The transition probabilities and the lifetimes have been calculated for the levels arising from magnetic exchange coupling in the following electron spin pairs: SA = ½-SB = ½; SA = ½-SB = 1; SA = ½-SB = 32; SA = 1-SB = 1. Such transition probabilities and lifetimes have been expressed as a function of the relaxation properties of the uncoupled spins in the assumption that magnetic coupling does not provide further relaxation pathways, and that the coupling frequency is large with respect to the electron relaxation rates of both spins. From the above values, nuclear relaxation as a function of the intensity of the external magnetic field has been calculated for nuclei dipole-coupled with either electron spin. The calculated nuclear relaxation dispersion has been then analyzed in terms of an "effective" electron relaxation time, the knowledge of which is important for NMR of magnetic coupled systems. The calculations provide a basis for understanding electron relaxation in magnetic-coupled dimers. Comparison with available experimental literature data is presented. Copyright 1998 Academic Press. Copyright 1998 Academic Press