The paper offers a new estimate of the sensitivity of Italy's primary budget balance to macroeconomic variables. The analysis has distinguishing features: detailed itemization of public finance aggregates; close attention to the statistical properties of the time series; and joint estimation of elasticities with respect to both real GDP and inflation. First, the economic variables driving the automatic component were chosen. Second, when possible, a macroeconomic base was associated with each public finance item. Third, each tax base was regressed on the driving economic variables. Fourth, each budget item that was supposed to include an automatic component was regressed either on its own base or directly on the economic variables affecting the automatic components. The effects on public budget are simulated to investigate the consequences of a change in nominal and real GDP.