A constitutional analysis is presented of the Establishment Clause of the First Amendment of Senate Bill 550, the Packwood-Moynihan proposal for federal tuition tax credits for parents who pay tuition in order to send their children to a nonpublic school. The Supreme Court has developed a three-part standard under the Establishment Clause: the legislation must have a secular purpose and a secular effect and it must not create excessive entanglements between government and religion. With respect to the secular purpose requirement, the articulated purpose of the Packwood-Moynihan proposal is to promote educational (not religious) pluralism and to enhance educational opportunity for all Americans at their chosen schools. The entanglements test has two concerns: whether legislation creates undue administrative involvements between church and state; and whether it fosters serious political divisiveness or fragmentation along religious lines. It is suggested that whereas the secular purpose and entanglements tests should not threaten the validity of federal tuition tax credits, the secular effect requirement presents a more difficult question. Attention is directed to the Committee for Public Education v. Nyquist decision, which invalidated New York's tuition tax benefit program. Among the arguments favoring the bill are the following: the proposal would grant assistance to individuals, not institutions; it proposed national tax legislation in line with the power of Congress to tax and spend; aid can be viewed as going to nonideological secular functions of church-related schools; and the legislation might help reserve freedom of educational choice which the Supreme Court has held is constitutionally protected. The text of the bill is appended. (SW)