A method of deriving sea ice concentrations from the 0.81-cm wavelength radiances of the Nimbus 7 scanning multichannel microwave radiometer (SMMR) is described and used in a comparative study of the Bering Sea ice ocver during March 1979. Case studies during 2 days in March demonstrate the utility of the SMMR for studying marginal ice zone processes. The first day provides an example of ice divergent conditions with winds from the northeast advecting the ice southwest toward the ice edge. Comparison of the SMMR-derived ice concentration maps with surface, aircraft, and Tiros-derived ice charts shows that the microwave data give the ice edge position to within 30 km, corresponding to the highest spatial resolution of SMMR. The SMMR ice concentrations also give an accurate description of the general morphology of the ice cover including the presence of ice shore polynyas. The second day illustrates the effect of a storm passage on the ice cover. The SMMR ice map for this day correctly describes the retreat of the ice cover and gives the positions of local regions of open water and of high ice concentration within the park. The two examples show that for the Bering Sea the SMMR algorithm provides accurate large-scale to mesoscale data on both the ice edge position and the location of low and high ice concentration regions.