The object of this article is to show some of the legal arguments of the unconstitutionality of the Colombia-United States Trade Promotion Agreement (tlc) signed in Washington on September 22, 2006. The TLC is unconstitutional because it legitimizes biopiracy in the chapter on patents and, in consequence, it infringes the national interest of Article 81 of the Political Constitution. Colombia’s national interest in the area of genetic resources is based on the objective conditions and the material characteristics of the Colombian State, recognized as one of the world’s major centers of biological diversity. The legal regulations of the ecological aspects of this are set out in the Political Constitution, under Law 99 of 1993, Law 165 of 1994 and Decisions 391 and 486, from the Doha Round and of the defensive and offensive interests of Colombia in the tlc, both of which are preferential to Colombia.