The response of agriculture to changes in relative prices is an important factor in the success of structural adjustment programs in Africa. In this paper I estimate supply functions for total agricultural output, food crops and export crops in 14 African countries for the years 1975 to 1990. Food and export crops are substitutes in production in the short run. Total agricultural output responds negatively to increases in export prices and positively to increases in food prices. A plausible explanation is that as farmers shift resources to export crop production, food supply falls in the short run, while the increase in export supply may take several years to materialize. The exchange rate is significant in explaining both food and export crop production and aggregate agricultural supply, suggesting that the exchange rate is acting as a proxy for excluded macroeconomic variables or that changes in the exchange rate are not passed immediately through to prices. © 2000 Elsevier Science B.V. All rights reserved.