In the present paper we estimate the impact of a biotechnology innovation in Spanish agriculture. Transgenic Bt maize offers the potential to control corn borers, that cause economically important losses in Spanish maize cultivation, more efficiently. Since 1998, Syngenta commercializes the varieties 'Compa CB' and 'Jordi CB', equivalent to an annual area of 20.000 ha, or an average adoption rate of 5,2% of Spain's total land allocation to maize. The profit increase engendered by this technological change during the four-year period 1998-2001 is estimated to be 8,7 million E for Spanish agriculture and 2,8 million E for Syngenta and the seed suppliers. The industry appears to be able to extract only one fourth of the total benefits. The lion share, i.e. three fourths, accrues to farmers.