The decision to release a new transgenic crop variety for planting in the European Union (EU) is a decision under irreversibility and uncertainty.  We use a real option model to assess the ex-ante incremental benefits and costs of the decision to release Bt maize and HT maize in the EU-15 member states.  The analysis uses Eurostat data for modelling the benefits and costs of non-transgenic maize using partial equilibrium models.  The farm-level benefits and costs of Bt maize and HT maize are derived from field trials conducted within the EU-funded ECOGEN project in combination with secondary data sources.  Adoption curves, hurdle rates and Maximum Incremental Social Tolerable Irreversible Costs (MISTICs) are calculated at country level for selected EU-15 member states.  In general, the results show that the MISTICs on a per capita level are very small confirming previous results calculated in values for the year 1995.  The MISTICs per farm are much larger.  This indicates a problem for decision makers.