In the present paper a bio-economic model was constructed to estimate the impact of a biotechnology innovation in EU agriculture. Transgenic Bt maize offers the potential to efficiently control corn borers that cause economically important losses in maize growing in Spain. Since 1998, Syngenta has commercialised the variety Compa CB, equivalent to an annual maize area of about 25 000 ha. During the 6-year period 1998-2003, a total welfare gain of 15.5 million euros was estimated from the adoption of Bt maize, of which Spanish farmers captured two thirds, the rest accruing to the seed industry.