The analysis is based on the direct relation of price level to money aggregates and to the index of economic activity (within the boundaries stipulated by model P*). The money market equilibrium is secured thanks to the standard demand for money function. Model specification was extended to include unemployment gap and oil prices. Despite this extension estimation results reveal the stationarity of stochastic components and yield strong support for the hypothesis of a mixed character of factors that affect prices. Empirical evidence was also found to expect a stable dependence between money demand and foreign direct investment.