We consider the performance of small and medium sized enterprises in Dutch horticulture under different environmental policy regimes across time. We address the question whether technical performance differs under these alternative regulatory regimes to test Porter's hypothesis that stricter environmental regulation reduces technical inefficiency. For this purpose, we use a stochastic production frontier framework allowing for inclusion of policy variables to measure the effect of alternative environmental policy regimes on firms' performance. The main result is that stricter environmental policy regimes have indeed reduced technical inefficiencies in Dutch horticulture. The estimation results indicate amongst others that the 1997 agreement on energy, nutrient and pesticides use enhances technical efficiency. Firms under the strict environmental policy regime are found to be more technically efficient than those under a lax regime, thereby supporting the claims by Porter and Van der Linde (Porter, M., Van der Linde, C., 1995. Green and Competitive: Ending the stalemate. Harvard Business Review 73, pp. 120-137) concerning Dutch horticulture. (C) 2006 Elsevier B.V. All rights reserved.