This paper seeks to explain the causes of the long-term variation in food and agricultural prices compared to the overall price level in the United States, over the period of 1974-1996. Using cointegration methods, this study confirms a general consensus of long-run neutrality of national money (money supply) and gives practical evidence of the real impact of international money (exchange rate) on the long-term variation of relative agricultural price in the United States, especially during the 1974-1988 period.