The purpose of this research memorandum is to describe a means of measuring racial balance and to apply the measure to the distribution of public school population in San Francisco. The measure is derived from the definition that full integration would be achieved if each school had exactly the citywide racial mixture of students. The racial balance index is so constructed that if every school had the citywide racial mixture, a value of 100 would result. If every school housed only one race (full segregation), a value of zero would result. Intermediate values reflect the degree to which the percentage of each race at each school varies from the citywide percentage of each race. This measure can also indicate not only the composite index for all four races (white, Spanish surname, black, and Oriental), but also the degree of integration achieved for an individual race. The measure takes into account school size. (Author/EB)