Aggregated Social Accounting Matrices (SAMs) will be built for the Portuguese economy in 1997, 1998 and 1999, based on the country’s national accounts statistics. The SAMs will be shown as a working instrument for quantifying the flows in the economic circuit and for simulating the effects resulting from changes in such flows. The economic flows associated with the government subsectors will be emphasised, whilst accounting and fixed-price multipliers will be calculated to facilitate the study of the effects resulting from changes in the government’s expenditure, which will also be subjected to a test on their veracity.