We examine the determinants of the adoption of genetically modified (GM) corn and soybean varieties by Iowa producers using data collected from a survey of producers. The representative respondent increased or held constant his GM soybean acreage but decreased his GM corn acreage. Agreement with the statement that consumers will not accept some bioengineered foods was associated with a significant decline in the intended share of acreage devoted to GM corn but had no explanatory power for GM soybean planting intentions. Risk attitudes did not prove to be a significant explanatory factor, perhaps due to the existence of production risk and price risk, which may have offset each other in the acreage allocation decision. Other significant factors included gross farm income, the previous year’s acreage allocation, agreement with the statement that farmers will benefit from biotechnology, years of schooling (soybeans only), total corn acreage (corn only), and concern regarding European corn borer yield damage (corn only). An increase in gross farm income was associated with an increase in the share of GM acreage for both crops. The previous year’s GM acreage share for that crop was highly significant.