We report on spin blockade observed in several different lateral quantum dot systems. We observe the typical features of alternating position and amplitude of Coulomb peaks as a function of a magnetic field perpendicular to the sample surface. In a nonlinear regime strong negative differential conductance is observed with a striking regularity. This is not a universal behaviour. Instead we propose a complex interplay of spin blockade, electron interaction and relaxation. At strong tunnel coupling to the leads we use spin blockade as a spectroscopy tool to reveal the spin configuration in a Kondo regime with a pronounced chessboard pattern. By comparing measurements of different samples we find that Kondo effect and spin blockade can be combined in two different ways depending on the spin configuration of the dot. Thus the combination of both effects can be used to detect spin polarized filling of dot orbitals instead of regular filling.