Previous studies have shown that the microwave brightness temperature (T_B) of snow and firn increases markedly as the surface becomes wet (e.g. Stiles and Ulaby, 1980; and Zwally and Gloersen, 1977). For example, the T_B at station Dye II (66.5N, 46.2W), on the Greenland ice sheet, as observed by the Nimbus-5 microwave radiometer, increases abruptly from 170 K to 245 K. during the summer melt period (Zwally, 1984). Now the Nimbus-5 microwave data are analysed, using T_B change criteria to map the extent and duration of summer melting of the surface of the Greenland Ice Sheet and several Antarctic ice shelves during 1973-1976. Inter-annual variations in the melt pattern are notable and several events are described in which the increased T_B during the month of January outlines the ice streams flowing from West Antarctica into the Ross Ice Shelf.