Corn acreage response in Iowa is examined using a time-varying parameter regression model. Separate estimates of the permanent portion of the parameter vector are obtained for each year over the period 1957-82. The estimated elasticities are grouped into "program" and "nonprogram" periods. The results indicate corn acreage response is more own-price elastics, and the elasticity is less variable under government acreage control programs than under a "nonprogram" regime. The assumption of parameter constancy is shown to be inappropriate for modeling Iowa corn acreage response over time.