Antarctic sea ice concentrations and extents, derived from the satellite passive microwave data of the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) are close but not identical depending on which of two major algorithms is used in the calculations. Overall, ice extents tend to be higher and ice concentrations lower when determined from the AMSR-E bootstrap algorithm (ABA) than when determined from the enhanced NASA team (NT2) algorithm, although the differences are within the algorithm error bars. Both algorithms obtain similar negative slopes for the lines of linear least squares fit through the short (4.5-year) AMSR-E data record available so far. When the ABA results are compared with results from the bootstrap algorithm applied over the same time period to data from the Special Sensor Microwave Imager (SSM/I), the two bootstrap results, from different satellites and different instruments, match even more closely than the ABA versus NT2 results from the same AMSR-E instrument. This is encouraging and is likely due to considerable effort to minimize the AMSR-E versus SSM/I bootstrap differences, in consideration of extending the SSM/I record (which goes back to 1987) with the AMSR-E results.