We analyzed brightness variations in widespread dimming regions occurred in several major eruptive events in 2003 and 2005 resulted in fast halo CMEs. In all cases brightness of remote dimming regions show some pre-eruptive growth, then gradual and fast decrease to minimum. The time interval of maximal decrease overlaps with X-flare peak and LASCO CME onset. Brightness variations in some dimmed regions are highly correlated before the CME onset and much less – after. It suggests a break of magnetic connectivity between previously linked coronal structures. Dimmings develop similar at 175 and 195 Å being shallower and sometimes delayed at 304 Å. In large-scale region (L$>$0.5 $R_\odot$) dimming propagates with a speed of $\sim$ 250 km/s which is typical for EIT-waves.