Local neutrality is normally assumed in calculating the distributions of point detects and the I-V relations in systems, in which the defects are mobile, though the Poisson equation with a nonzero space charge is the exact condition to be used. The question when local neutrality holds, al least approximately, and can be used in the analysis, is examined here. It is shown that local neutrality prevails (approximately) as long as gradients in the concentration of the majority charged defects are small. Measures for these gradients are given for representative models. It is shown that these gradients may be of different origin. They can be caused by non uniform doping, electrical field, gradient in chemical potential and a combination of these factors.