Racial residential segregation persists at high levels in all American cities with sizeable black populations. In 1980, 28 cities with black populations of more than 100,000 were home for 9.7 million blacks, more than a third of all American blacks. The average segregation index score for these cities was 81, when 100 means that every city block is either 100 percent black or 0 percent black. Neither the size of the black population nor its percentage of the total city population can be used to predict how segregated a city is. Racial exposure measures, which calculate the extent to which blacks are exposed to nonblack residents in their home neighborhoods, and similarly, nonblacks to black residents, also indicate the extent of racial segregation in the 28 cities. The 1980 average segregation index score has declined from the 87 of 1970, thus continuing the trend that was apparent in the 1960s. More rapid declines are possible, as shown by 8 individual city scores which declined by over 10 points. Seven cities, however, failed to decline by more than two points. Reasons for the differences are not known. (CMG)