We have analyzed H \alpha Fabry-Perot interferograms of NGC 5457 ( M101 ) in order to calculate the rotation curve .
We have also isolated a sample of 263 HII regions and we determined for each one its radial velocity and velocity dispersion .
The rotation curve agrees with previous determinations and the mass derived from it is 9.8 \times 10 ^ { 10 } M _ { \odot } .
The distribution of velocity dispersion values of the HII regions presents a normal behavior , with a mean value of 30 km sec ^ { -1 } .