  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.
