This paper tests a reduced form equation in which real GNP for the United States is explained by deviations of multi-period M1 growth rates from ex ante expectations of those rates formed from one to eight quarters earlier. The theoretical model is suggested by Stanley Fischer's 1977 article, and may be thought of as a 'New Keynesian' model. The equations are tested in both level and first difference specifications, to allow for possible unit roots. Empirical results strongly support this model in preference to 'New Classical' and 'Keynesian' alternatives. Ex ante expectations or M1 growth are formed from multi-period forecasts made by Chase Econometrics, Inc., between 1970 and 1979.