The shrinkage is a significant phenomenon in concrete structures. The article is aimed at monitoring the shrinking of concrete slabs under laboratory conditions. The results of laboratory research aimed at unreinforced slabs strains affected by the non-homogeneity of concrete are mentioned in the article. According to these results another research of shrinkage influence on strains and deflection of concrete slabs reinforced by steel, resp. GFRP reinforcement has been prepared. The results of this research confirm the significant effect of concrete non-homogeneity on the formation of strains and deflections due to shrinkage.