Centrally planned economies (CPEs) account for about a third of the world's population and about a fourth of its output. In view of their importance in the world economy, they need to be included in international comparitive studies. Their inclusion, however, presents problems for several reasons. First, CPEs report net material product, not gross national product (GNP). Also, their prices are set and exchange rates are set administratively, so that conversion to dollars is problematic. Finally, they compute growth rates using methods that in most cases are strongly upward biased. This report tries to identify and evaluate alternative methods for computing the levels and growth rates of the GNPs of centrally planned economies and to undertake illustrative benchmark year computations.