National and regional acreage supply functions are developed for soybeans utilizing data from 1948 to 1973. Particular attention is given to the measurement and analysis of the effects of government commodity price-support programs on harvested soybean acreage. Detailed attention is given to the effects of the feed grain programs of the 1960' s and to the set-aside programs of 1971-73. The main emphasis is placed on the calculation of "effective" prices of soybeans and competing crops and the ability of the model to project harvested acreage 6-9 months in advance.