Passive microwave data at 1.55 cm collected by the Nimbus 5 Electrically Scanning Microwave Radiometer are analyzed to determine the areal extent and distribution of Arctic sea ice at the time of transition from summer melt to fall freeze up of years 1973--1976. While regional variations are great, the total areal coverage of ice-laden sea changes interannually only about 2% from 7¿106 km2. Ice surviving the summer melt has a mean concentration of 0.74 and a volume of 15.8¿103 km3, both somewhat lower than earlier estimates. Multiyear ice concentrations were measured by examining on grid cells of 200 km dimension the brightness changes associated with freezing of leads. A significant spatial variation in multiyear ice emissivity was observed which brought about spatial brightness variation comparable to that caused by typical mixtures with open water and first-year ice, Measurement errors made the detail of interannual changes in emissivity suspect.