The proposed treaty between the United States and Mexico represents a commendable attempt to alleviate the difficulties which arise when the nations of one country are imprisoned in another. At least one aspect of the treaty raises serious constitutional questions, however. Article VI of the treaty prohibits any American court from entertaining challenges by transferred Americans to the Mexican sentences being served. Because some of these challenges could be based on American constitutional grounds, article VI appears to deprive American courts of the power to hear a category of constitutional claims. The constitution's requirement is only that some court, Federal or State, be available to hear constitutional claims by those claiming illegal imprisonment. The constitutional infirmity created in the treaty can, however, be cured if, prior to transfer, each prisoner waives any future right to attack in an American court the validity of his or her Mexican trial. The constitutionality of the treaty depends on the effective implementation of article IV, paragraph 2, and article V, paragraph 1, which provide for the prisoners' express consent to be given voluntarily and with full knowledge of the consequences thereof as a precondition to their transfer. In some circumstances, however, conditioning transfer on a waiver of American collateral attack rights might violate the unconstitutional conditions doctrine, which limits the power of the Government to condition the conferral of a benefit upon the surrender of a citizen's constitutional rights. While the doctrinal test has not been precisely defined, the courts seem to require that the relinquishment of rights be directly related to the public interest; that the citizen not be required to surrender any more rights than are absolutely necessary to serve the public interest, and that the citizen willingly accept the condition upon which the benefit is predicated. Steps should be taken to ensure that the procedural implementation of the waiver meets these conditions.