We estimated absolute shifts of Fe I and Fe II lines from Fourier-transform spectra observed in solar active regions .
Weak Fe I lines and all Fe II lines tend to be red-shifted as compared to their positions in quiet areas , while strong Fe I lines , whose cores are formed above the level \log \tau _ { 5 } \approx - 3 ( about 425 km ) , are relatively blue-shifted , the shift growing with decreasing lower excitation potential .
We interpret the results through two-dimensional MHD models , which adequately reproduce red shifts of the lines formed deep in the photosphere .
Blue shifts of the lines formed in higher layer do not gain substance from the models .