Keith M. Carlson discusses the nature and extent of the Commerce Department’s recently released revision of the nation’s income and product accounts. The article focuses on the effect of the Department’s revision on nominal GNP, output, and prices, and finds that, over the 1948-84 period, the revision had large effects on the levels of these variables, but very little effect on their rates of change. In addition, Carlson found that the revision had only a marginal effect on econometric estimates of certain key macroeconomic relationships.